Review Article

CONTROL OF PLANT HEIGHT BY HETEROTRIMERIC G-PROTEIN ΑLPHA SUBUNIT IN RICE

Y. Chen^1,2, J. Wei², Y. Zhang², G. Li², B. Lü², and L. Liu¹*

¹ Jiangsu Key Laboratory of Crop Genetics and Physiology/Jiangsu Co-Innovation Centre for Modern Production Technology of Grain Crops/Jiangsu Key Laboratory of Crop Genomics and Molecular Breeding/Key Laboratory of Plant Functional Genomics of the Ministry of Education, Yangzhou University, Yangzhou 225009, China

² College of Bioscience and Biotechnology, Yangzhou University, Yangzhou 225009, China

^* Corresponding Author’s Email: ljliu@yzu.edu.cn

ABSTRACT

Plant height is an important agronomic trait in rice that affects rice morphogenesis, apical dominance, harvest index and yield. Rice plant height is controlled by genes that lie in a complex regulatory network. At present, many plant height-related genes have been identified in rice, among which heterotrimeric G-protein α subunit, RGA1, is an important regulator. RGA1 is involved in cell division and regulates internode cell number, and in the biosynthesis and responses to phytohormones gibberellin (GA) and brassinosteroid (BR) signalling that regulates stem and internode elongation. Additionally, RGA1 affects rice plant height via the effect on nitrogen uptake and utilization and the interaction with drought stress responses. This review summarizes the progress on the regulation of rice plant height by RGA1 and proposes a focus of future research on the influence of RGA1 on rice plant height. We hope to provide a theoretical foundation for elucidating the regulatory mechanism of plant height and the application of RGA1 in the genetic improvement of plant height for a high and stable grain yield in rice production. We also propose new ideas for revealing the integral functions of G-proteins in rice.

Key words: RGA1, Plant height, Hormone, Nitrogen, Drought, Rice.

https://doi.org/10.36899/JAPS.2021.5.0321
Published online January 21, 2021

INTRODUCTION

The first 'Green Revolution' introduced the term semi-dwarfing, effectively solved issues such as rice resistance to lodging and achieved an increase in rice yield and stable rice production (Athwal et al., 1971; Evenson and Gollin, 2003; Ferrero-Serrano et al., 2019). Plant height is an important factor that affects rice morphogenesis, apical dominance, biomass, lodging resistance, pest resistance, and harvest index (Asano et al., 2011; Liu et al., 2018). Rice plant height architecture is a result of the interactions between genes and the environment. It is determined by 2 aspects, external and internal factors. First, it is influenced by environmental factors, such as drought stress and the application of nitrogen fertilizers. Second, it is regulated via the major and minor genes controlling plant height. These genes are involved in the regulation of plant hormone signalling pathways that are tightly associated with plant height, including gibberellins (GAs) and brassinosteroids (BRs) (Asano et al., 2011; Liu et al., 2018). Through genetic analysis, scientists have obtained a large number of rice dwarf mutants, including mutants related to GA signalling (d18, d35) and BR signalling (d2, d11) and mutants with the absence of G-protein α subunit (Gα) (d1, d89) (Ashikari et al., 1999; Hong et al., 2003; Itoh et al., 2004; Yang et al., 2014).

RGA1 is the rice heterotrimeric G-protein alpha subunit and is involved in many signal transduction pathways that regulate plant height in rice (Liu et al., 2018; Wang et al., 2019). This review describes the structure and function of RGA1, with a focus on RGA1 participating in rice hormonal signal transduction, responses to nitrogen and drought stress pathways, and discusses the physiological and molecular mechanism of plant height regulation by RGA1 in rice. Our goal is to provide a reference for an in-depth understanding of the rice heterotrimeric G-protein system and the application of RGA1 in rice genetic breeding.

The structure of the RGA1 protein: Rice has a single Gα subunit, designated RGA1 or DAIKOKU DWARF1 (D1/d1). In 1990, Ma et al. cloned the first plant G-protein α subunit, AtGPA1, from Arabidopsis thaliana (Ma et al., 1990). In 1995, Seo et al. used ArabidopsisGPA1 cDNA as a probe and cloned the G-protein α subunit (RGA1) in rice IR 36 for the first time (Seo et al., 1995). The full-length cDNA of RGA1 is 1173 bp and contains 13 exons (Fig. 1a). The RGA1 gene encodes 390 amino acids and contains many conserved sequence loci, including the N-myristoylation site, the casein kinase II phosphorylation site, the ATP/GTP-binding motif (P-loop), the tyrosine kinase phosphorylation site, the G1-5 box, the receptor binding site, the GTP/Mg²⁺ binding site, the Switch I and II region, the GoLoco-binding site, the G-protein βγ subunit complex (Gβγ) interaction site, and the adenylyl cyclase interaction site (Fig. 1b). The RGA1 protein contains 2 domains, a C-terminal GTPase domain (Ras-like domain) and an N-terminal α-helical domain (Fig. 1c). It has a molecular weight of 45.2 kDa and an isoelectric point of 6.62 (Fujisawa et al., 1999; Yadav et al., 2013). Different from that in Arabidopsis, RGA1 in rice does not contain a regulator of G-protein signalling (RGS) protein interaction site, similar to that in animals. RGA1 has a self-activation/deactivation, nucleic acid-dependent regulatory mechanism. Thus, rice is an ideal model plant species to discover the regulatory mechanism of new activation (Temple and Jones, 2007; Biswal et al., 2019).

Function of the RGA1 protein in rice: RGA1 can function independently or coordinate with the G-protein β subunit (Gβ) and γ subunit (Gγ) to mediate the transduction of many extracellular signals to intracellular signals and regulate various physiological activities (Urano et al., 2013; Sun et al., 2018). The earliest study of RGA1 function in rice was conducted in the d1 mutant. In 1999, Ashikari et al. discovered the rice dwarf mutant Daikoku, and through map-based cloning, they isolated and identified the gene associated with the dwarf phenotype. This study showed that the responsible gene was located on rice chromosome 5 and encoded RGA1, which was later named Dwarf 1 (d1) (Ashikari et al., 1999). RGA1 was expressed in all rice tissues tested (Izawa et al., 2010). Together with previous studies, it was determined that RGA1 is involved in cell division, hormonal signal transduction pathways, abiotic stress responses, resistance to rice blast, and nitrogen uptake and utilization in rice (Table 1).

Table 1.Functions and biochemical/molecular responses of RGA1

RGA1 regulates signal transduction pathways related to plant height in rice: d1, the loss-of function mutant of the gene for rice RGA1, is the first studied Gα mutant rice, and produces a dwarf phenotype. Studies have found that RGA1 directly or indirectly regulates rice plant height through its involvement in cell division, responses to hormones and drought, and nitrogen uptake and utilization.

Involvement of RGA1 in cell division to regulate rice plant height: The discovery of and research involving plant Gα were first done in Arabidopsis. Arabidopsis G-protein α subunit, GPA1, positively regulates cell division; thus, gpa1 mutants exhibit shorter hypocotyls and smaller seeds (Ullah et al., 2001). Oki et al. conducted a comparative analysis of 10 rice strains with rga1 mutations and found that compared with the wild type, the absence of RGA1 resulted in a 25%-50% decrease in plant height. Additionally, the rice strains with rga1 mutations exhibited erected panicles, darkened leaf colour, and small rounded seeds (Oki et al., 2009b). Compared with the wild type, d1 decreased plant height by 52%, seed size by 25%, and leave size by 50% (Urano et al., 2016). d1-5 shortened the internode length and decreased the number of cells but did not change the average cell length (Izawa et al., 2010). Therefore, the dwarf phenotype of the d1 mutant is mainly caused by a reduction in the number of cells in various organs (Oki et al., 2005; Izawa et al., 2010). However, Yang et al. found that compared with the wild type, the d89 mutant (d89 represents a metastable epigenetic mutant of the D1 locus in indica cultivar MU101) resulted in severely shortened internodes and significant elongation of cell length in the first internode, leading to a significantly decreased cell number (Yang et al., 2014). Results from these studies showed that different RGA1 mutants exhibited different responses in internode cell division. RGA1 is a positive regulator of cell elongation, and the absence of RGA1 results in shortened internode length, leading to dwarfing in rice RGA1 mutants.

Involvement of RGA1 in the GA signalling pathway to regulate rice plant height: GA is an important hormone that regulates plant growth and development. It promotes seed germination, induces the activity of α-amylase, and stimulates internode and stem elongation (Ayano et al., 2014; Hedden and Sponsel, 2015; Binenbaum et al., 2018). The control of rice plant height is mostly related to the biosynthesis of and responsiveness to GA (Ashikari et al., 2002; Liu et al., 2018). d1 was identified as a GA-insensitive mutant (Ashikari et al., 1999). The external GA₃ concentration for inducing internode elongation in rice d1 mutants was 100-fold higher than that in wild-type rice plants, and d89 did not respond to elongation of the aboveground portion induced by external GA (Ueguchi-Tanaka et al., 2000; Yang et al., 2014). This indicated that RGA1 is involved in responses to GA signals in rice, and the absence of RGA1 led to reduced sensitivity GA signals in plants, which inhibited stem elongation (Liu et al., 2018). The GA-GID1-DELLA pathway, which is the basic GA signal transduction pathway, has been established. The GID1 gene encodes a soluble GA receptor, and the SLR1 gene encodes a DELLA protein, which is a repressor of GA signalling, mediating GA signalling in rice. Until recently, the molecular mechanisms governing the repression of GA signalling by DELLA proteins were unknown. It is now revealed that DELLA proteins interact with various transcription factors, and through these interactions, regulate the transcription of genes involved in GA response. Several DELLA targets have already been identified in Arabidopsis and only a few in rice (Hedden and Sponsel, 2015; Daviere and Achard et al., 2016). The identical phenotypes in the single slr and double slr/d1 mutants indicate that the D1 product functions as a member of the same GA-signalling pathway as the SLR protein (Ikeda et al., 2001; Ueguchi-Tanaka et al., 2005; Iwasaki et al., 2003). The DNL1 was a regulator in the GA responsiveness and signal transduction pathway, and the expression of D1 was significantly decreased in dnl1, a dwarf and narrow-leaf mutant (Wei et al., 2013). However, how rice perceives GA and how the GA signal is transmitted to cause GA-regulated plant growth are still not well known.

In addition to components in GA signalling, endogenous GA levels regulated by the GA metabolism also have an important role in the control of plant height. Many GA-related genes are feedback or feedforward regulated by bioactive GAs, where GA20ox and GA3ox function in GA biosynthesis with feedback regulation, and GA2ox functions in GA catabolism with feedforward regulation by bioactive GAs (Zhang et al., 2008). The dwarf phenotype of d1 mainly presents severely shortened second and third internodes, especially the second internode. However, in the second and third internodes of rice d1 mutants, the expression of Os20ox was 6- and 4.5-fold higher than that in wild-type rice plants, respectively. Ueguchi-Tanaka et al. indicated that the feedback inhibitory effect of active GA on Os20ox was absent in RGA1-absent internodes (Ueguchi-Tanaka et al., 2000). The mechanism of RGA1 function involving in GA signalling to regulate rice height is showed in Fig. 2a.

Involvement of RGA1 in the BR signalling pathway to regulate rice plant height: BR is also proven to be an important hormone that regulate plant height (Nagai et al., 2018). Rice mutants insensitive to BR or defective in BR signalling also exhibit a dwarf phenotype (Mori et al., 2002; Hong et al., 2003; Tanaka etal., 2009; Nakagawa et al., 2012; Hu et al., 2013; Castorina and Consonni, 2020). Compared with the wild type, mutant d1 and d61-1 were insensitive to 24-epiBL (24-epibrassinolide, external BR analogue) in the stimulation of coleoptile elongation (Wang et al., 2006). Compared with wild-type T65, mutant T65d1 exhibited lower sensitivity to 24-epiBL (Oki et al., 2009a). This indicates that RGA1 is involved in the responses to BR signals in rice and that the absence of RGA1 causes insensitivity to BR and inhibits coleoptile elongation.

The levels of mRNAs for BR-biosynthetic genes D2, D11, and DWARF were all reduced in rice d1 mutants and wild-type rice plants T65d1 by application of 24-epiBL. Since the feedback regulation with 24-epiBL in the T65d1 mutant is not impaired, RGA1-mediated internode elongation seems not be connected directly with the BR cascade via rice BR receptor, BRI1 (Oki et al., 2009a; Tanaka et al., 2009). TUD1, a U-box E3 ubiquitin ligase, can directly downregulate D1, thereby mediating the BR signalling pathway. In rice tud1-2 mutants, the dwarf phenotype in the second internode was the same as that in BR-defective mutants d61 and brd1; BRD1, DWARF4, and D61, genes related to BRI1-mediated BR signalling, had significantly higher expression levels in the second internode than in the first internode. Thus, BR signal transduction mediated by D1-TUD1-BU1 pathway may parallel or partially overlapped with the canonical BRI1-mediated BR signal transduction and its regulation of plant height (Hu et al., 2013; Tong et al., 2014). The relationship among RGA1, TUD1, BU1and BRI1 is shown in Fig. 2b.

Involvement of RGA1 in the regulation of nitrogen to affect plant height: Nitrogen is one of the macronutrients necessary for the growth and development of crops. It is an important component for maintaining normal metabolism and the cycling and distribution of substances in crops. Additionally, nitrogen fertilizer is a crucial factor that influences plant height (Ali et al., 2018; Yang et al., 2020). Sun et al. constructed a series of near-isogenic lines carrying DEP1 (encoding Gγ and regulating seed development) as well as single and double DEP1 and D1 mutants. They found that different DEP1 alleles exhibited different responses to nitrogen. The vegetative growth of rice RGA1 mutants was insensitive to nitrogen, and nitrogen content increased. Rice dep1-d1 double mutants exhibited a severe dwarf phenotype (Sun etal., 2014). The molecular mechanism of the interaction between RGA1 and DEP1 is still unclear; therefore, an in-depth investigation of the coordination between DEP1 in seed development and RGA1 in the formation of plant height can provide new ideas for increasing nitrogen utilization efficiency and rice yield.

Involvement of RGA1 in the influence of drought stress on rice plant height: The interaction between genes and the environment is ubiquitous phenomenon. Genetic and physiological traits often change with the interaction with environmental variables. Drought is an important stress for rice. A limited water supply often inhibits height development, consequently affecting yield (Zhuang et al. 1997; Oladosu et al., 2019). Lots of studies performed on the gene × environment interaction of agronomic traits, as grain filling, panicle size, root growth and plant height, most of which focusing on the genetic effects of QTLs (Zhuang et al., 1997; Pandey and Shukla, 2015; Oladosu et al., 2019). So far, few reports have documented the RGA1 function for rice height combined with drought stress. Droughted d1 plants showed a significantly higher root to shoot ratio than the wild-type rice under the identical drought conditions, while this ratio did not differ between genotypes in the absence of drought. d1 had a lower leaf temperature, higher stomatal conductance, and higher photochemical reflectance index, resulting in lower sensitivity to drought stress (Ferrero-Serrano and Assmann, 2016; Ferrero-Serrano et al., 2018). Jangam et al. performed microarray analysis in combination with the STIFDB 2.0 database and obtained 106 differentially expressed genes related to drought stress between wild-type rice plants and d1 mutants. Among them, 13 genes were significantly associated with drought, including heat shock protein, MAP kinase and transcription factors, etc (Jangam et al., 2016). This indicated that the absence of RGA1 led to an increase in the photochemical reflectance index, disrupted the expression of drought stress-related genes, and increased drought resistance in rice d1 mutants. These results deepen the understanding of the mechanism of RGA1 in response to drought stress and provide references for plant type improvement and drought resistance breeding in rice.

Future prospective: Early studies on RGA1 in rice mostly focused on the phenotype and physiological characteristics of mutants. In recent years, substantial progress has been made in the molecular mechanisms of RGA1 in regulating plant height by participating in hormone signalling and nitrogen utilization. For the regulation of plant height by RGA1 in rice, future studies should address the following areas:

Strengthen research on the mechanism of how RGA1 affects plant height by regulating hormones: Hormones that affect the formation of plant height include GA, BR, IAA (an auxin), abscisic acid (ABA), and strigolactones. Past studies have described, in depth, the mechanism of RGA1 regulation of rice plant height through the GA and BR signal transduction pathways. Very few reports have addressed the role of RGA1 in the regulation of plant height by other hormones. Thus, is RGA1 involved in the signal transduction pathway of other hormones to regulate plant height in rice? The mechanism of the interaction between RGA1 and various hormones in the regulation of plant height needs to be further studied.

Improve the G-protein signalling network and further elucidate plant height regulation mechanisms in rice: RGA1 is a membrane protein. It can function alone or interact with Gβ and Gγ to regulate intracellular signal transduction. Clarification of the associations between G protein and each signalling pathway is necessary for constructing and improving the enormous G-protein signalling network. Additionally, to reveal the detailed mechanism of RGA1 regulation of rice plant height, it is urgent and necessary to utilize the massive genetic resources (new genes, mapping populations, near-isogenic lines, introgression lines, recombinant inbred lines, double haploids, etc.) and advanced 'omic' technologies to analyse the upstream regulatory proteins and downstream effectors and their functions. It is also necessary to discuss the functions of RGA1 in rice stem development under different environmental conditions and growth stages.

Strengthen research on rice plant height regulation by RGA1 under abiotic stresses: In recent years, extreme abiotic stresses (such as drought and heat) have occurred frequently and are posing significant impacts on the growth, development, and yield of rice. However, there is a lack of research on how RGA1 is expressed and how it affects rice plant height under these abiotic stresses. In the future, it is necessary to strengthen research on the expression patterns of RGA1 under extreme drought, high temperature, and multiple stresses during the rice vegetative growth period and to determine how RGA1 regulates plant height plant to adaptation to the environment, with a goal of providing a reference for achieving a high and stable rice yield.

Acknowledgements: This research was funded by the Jiangsu Agriculture Science and Technology Innovation Fund, grant number “(cx(18)3007)”, the National Key Research and Development Program of China, grant number “2016YFD0300502” and “2017YFD0301206”, the National Natural Science Foundation of China, grant number “31671614” and “31871557”, and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

Authors’ contributions: Y. Chen, J. Wei, and L. Liu came up with the ideas and conceived the study. Y. Zhang, G. Li and B. Lü participated in its design and coordination. Y. Chen and J. Wei wrote the manuscript. L. Liu edited the manuscript. All authors read and approved the final manuscript.

References

1. Ali, J., Z. A. Jewel, A. Mahender, A. Anandan, J. Hernandez, and Z. Li (2018). Molecular genetics and breeding for nutrient use efficiency in rice. J. Mol. Sci. 19(6): 1762.
2. Asano, K., M. Yamasaki, S. Takuno, K. Miura, S. Katagiri, T. Ito, K. Doi, J. Wu, K. Ebana, T. Matsumoto, H. Innan, H. Kitano, M. Ashikari, and M. Matsuoka (2011). Artificial selection for a green revolution gene during japonica rice domestication. Proc. Natl. Acad. Sci. USA. 108(27): 11034–11039.
3. Ashikari, M., J. Wu, M. Yano, T. Sasaki, and A. Yoshimura (1999). Rice gibberellin-insensitive dwarf mutant gene Dwarf 1 encodes the α-subunit of GTP-binding protein. Proc. Natl. Acad. Sci. USA. 96(18): 10284–10289.
4. Ashikari, M., A. Sasaki, M. Ueguchi-Tanaka, H. Itoh, A. Nishimura, S. Datta, K. Ishiyama, T. Saito, M. Kobayashi, G. S. Khush, H. Kitano, and M. Matsuoka (2002). Loss-of-function of a rice gibberellin biosynthetic gene, GA20 oxidase (GA20ox-2), led to the rice ‘Green Revolution’. Breed. Sci. 52(2): 143–150.
5. Athwal, D. S. (1971). Semidwarf rice and wheat in global food needs. Rev. Biol. 46(1): 1–34.
6. Ayano, M., T. Kani, M. Kojima, H. Sakakibara, T. Kitaoka, T. Kuroha, R. B. Angeles-Shim, H. Kitano, K. Nagai, and M. Ashikari (2014). Gibberellin biosynthesis and signal transduction is essential for internode elongation in deepwater rice. Plant Cell Environ. 37(10): 2313–2324.
7. Binenbaum, J., R. Weinstain, and E. Shani (2018). Gibberellin localization and transport in plants. Trends Plant Sci. 23(5): 410–421.
8. Biswal, A. K., E. W. McConnell, E. G. Werth, S. F. Lo, S. M. Yu, L. M. Hicks, and A. M. Jones (2019). The nucleotide-dependent interactome of rice heterotrimeric G-Protein α-subunit. Proteomics. 19(9): e1800385.
9. Castorina, G., and G. Consonni (2020). The role of brassinosteroids in controlling plant height in Poaceae: A genetic perspective. J. Mol. Sci. 21(4): 16.
10. Daviere, J. M., and P. Achard (2016). A pivotal role of DELLAs in regulating multiple hormone signals. Mol. Plant. 9(1): 10–
11. Evenson, R. E., and D. Gollin (2003). Assessing the impact of the green revolution, 1960 to 2000. Science. 300(5620): 758–762.
12. Ferrero-Serrano, Á., and S. M. Assmann (2016). The α-subunit of the rice heterotrimeric G protein, RGA1, regulates drought tolerance during the vegetative phase in the dwarf rice mutant d1. Exp. Bot. 67(11): 3433–3443.
13. Ferrero-Serrano, Á., Z. Su, and S. M. Assmann (2018). Illuminating the role of the Gα heterotrimeric G protein subunit, RGA1, in regulating photoprotection and photoavoidance in rice. Plant Cell Environ. 41(2): 451–468.
14. Ferrero-Serrano, Á., C. Cantos, and S. M. Assmann (2019).The role of dwarfing traits in historical and modern agriculture with a focus on rice. Cold Spring Harbor Perspect. Biol. 11(11): 30.
15. Fujisawa, Y., T. Kato, S. Ohki, A. Ishikawa, H. Kitano, T. Sasakt, T. Asahi, and Y. Iwasaki (1999). Suppression of the heterotrimeric G protein causes abnormal morphology, including dwarfism, in rice. Natl. Acad. Sci. USA. 96(13): 7575–7580.
16. Hedden, P., and V. Sponsel (2015). A Century of gibberellin research. Plant Growth Regul. 34(4):740–760.
17. Hong, Z., M. Ueguchi-Tanaka, K. Umemura, S. Uozu, S. Fujioka, S. Takatsuto, S. Yoshida, M. Ashikari, H. Kitano, and M. Matsuoka (2003). A rice brassinosteroid-deficient mutant, ebisu dwarf (d2), is caused by a loss of function of a new member of cytochrome P450. Plant Cell. 15(12): 2900–2910.
18. Hu, X. M., Q. Qian, T. Xu, Y. Zhang, G. J. Dong, T. Gao, Q. Xie, and Y. B. Xue (2013). The U-box E3 ubiquitin ligase TUD1 functions with a heterotrimeric Gα subunit to regulate brassinosteroid-mediated growth in rice. PLoS Genet. 9(3): e1003391.
19. Ikeda, A., M. Ueguchi-Tanaka., Y. Sonoda, H. Kitano, M. Koshioka, Y. Futsuhara, M. Matsuoka, and J. Yamaguchi (2001). Slender rice, a constitutive gibberellin response mutant, is caused by a null mutation of the SLR1 gene, an ortholog of the height-regulating gene GAI/RGA/RHT/D8. Plant Cell. 13(5): 999–1010.
20. Itoh, H., T. Tatsumi, T. Sakamoto, K. Otomo, T. Toyomasu, H. Kitano, M. Ashikari, S. Ichihara, and M. Matsuoka (2004). A rice semi-dwarf gene, Tan-Ginbozu (D35), encodes the gibberellin biosynthesis enzyme, ent-kaurene oxidase. Plant Mol. Biol. 54(4): 533–547.
21. Iwasaki, Y., Y. Fujisawa, and H. Kato (2003). Function of heterotrimeric G protein in gibberellin signaling. Plant Growth Regul. 22: 126–133.
22. Izawa, Y., Y. Takayanagi, N. Inaba, Y. Abe, M. Minami, Y. Fujisawa, H. Kato, S. Ohki, H. Kitano, and Y. Iwasaki (2010). Function and expression pattern of the α subunit of the heterotrimeric G protein in rice. Plant Cell Physiol. 51(2): 271–281.
23. Jangam, A. P., R. R. Pathak, and N. Raghuram (2016). Microarray analysis of rice d1 (RGA1) mutant reveals the potential role of G-protein alpha subunit in regulating multiple abiotic stresses such as drought, salinity, heat, and cold. Plant Sci. 7: 11.
24. Lieberherr, D., N. P. Thao, A. Nakashima, K. Umemura, T. Kawasaki, and K. Shimamoto (2005). A sphingolipid elicitor-inducible mitogen-activated protein kinase is regulated by the small GTPase OsRac1 and heterotrimeric G-protein in rice. Plant Physiol. 138(3): 1644–1652.
25. Liu, F., P. D. Wang, X. B. Zhang, X. F. Li, X. H. Yan, D. H. Fu, and G. Wu (2018). The genetic and molecular basis of crop height based on a rice model. Planta. 247(1): 1–26.
26. Ma, H., M. F. Yanofsky, and E. M. Meyerowitz (1990). Molecular cloning and characterization of GPA1, a G protein α subunit gene from Arabidopsis thaliana. Natl. Acad. Sci. USA. 87(10): 3821–3825.
27. Ma, Y., X. Y. Dai, Y. Y. Xu, W. Luo, X. M. Zheng, D. L. Zeng, Y. J. Pan, X. L. Lin, H. H. Liu, D. J. Zhang, J. Xiao, X. Y. Guo, S. J. Xu, Y. D. Niu, J. B. Jin, H. Zhang, X. Xu, L. G. Li, W. Wang, Q. Qian, S. Ge, and K. Chong (2015). COLD1 Confers chilling tolerance in rice. Cell. 160(6): 1209–1211.
28. Mori, M., T. Nomura, H. Ooka, M. Ishizaka, T. Yokota, K. Sugimoto, K. Okabe, H. Kajiwara, K. Satoh, K. Yamamoto, H. Hirochika, and S. Kikuchi (2002). Isolation and characterization of a rice dwarf mutant with a defect in brassinosteroid biosynthesis. Plant Physiol. 130(3): 1152–1161.
29. Nagai, K., K. Hirano, R. B. Angeles-Shim, and M. Ashikari (2018). Breeding applications and molecular basis of semi-dwarfism in rice. In: Sasaki, T., and M. Ashikari (eds) Rice genomics, genetics and breeding. Springer (Singapore). 155–176.
30. Nakagawa, H., A. Tanaka, T. Tanabata, M. Ohtake, S. Fujioka, H. Nakamura, H. Ichikawa, and M. Mori (2012). SHORT GRAIN1 decreases organ elongation and brassinosteroid response in rice. Plant Physiol. 158(3): 1208–1219.
31. Oki, K., Y. Fujisawa, H. Kato, and Y. Iwasaki (2005). Study of the constitutively active form of the α subunit of rice heterotrimeric G proteins. Plant Cell Physiol. 46(2): 381–386.
32. Oki, K., N. Inaba, K. Kitagawa, S. Fujioka, H. Kitano, Y. Fujisawa, H. Kato, and Y. Iwasaki (2009a). Function of the α subunit of rice heterotrimeric G protein in brassinosteroid signaling. Plant Cell Physiol. 50(1): 161–172.
33. Oki, K., N. Inaba, , H. Kitano, S.Takahashi, Y. Fujisawa, H. Kato, and Y. Iwasaki (2009b). Study of novel d1 alleles, defective mutants of the α subunit of heterotrimeric G-protein in rice. Genes Genet. Syst. 84(1): 35–42.
34. Oladosu, Y., M. Y. Rafii, C. Samuel, A. Fatai, U. Magaji, I. Kareem, Z. S. Kamarudin, I. Muhammad, and K. Kolapo (2019). Drought resistance in rice from conventional to molecular breeding: A review. Int. J. Mol. Sci. 20(14): 3519–3540.
35. Pandey, V., and A. Shukla (2015). Acclimation and tolerance strategies of rice under drought stress. Rice Sci. 22(4): 147–161.
36. Peng, P., Y. D. Gao, Z. Li, Y. W. Yu, H. Qin, Y. Guo, R. F. Huang, and J. Wang (2019). Proteomic analysis of a rice mutant sd58 possessing a novel d1 allele of heterotrimeric G protein α subunit (RGA1) in salt stress with a focus on ROS scavenging. Int. J. Mol. Sci. 20(1): 167.
37. Seo, H. S., H. Y. Kim, J. Y. Jeong, S. Y. Lee, M. J. Cho, and J. D. Bahk (1995). Molecular cloning and characterization of RGA1 encoding a G protein α subunit from rice Oryza sativa Plant Mol. Biol. 27(6): 1119–1131.
38. Steffens, B., and M. Sauter (2009). Heterotrimeric G protein signaling is required for epidermal cell death in rice. Plant Physiol. 151(2): 732–740.
39. Steffens, B., and M. Sauter (2010). G proteins as regulators in ethylene-mediated hypoxia signaling. Plant Signal. Behav. 5(4): 375–378.
40. Suharsono, U., Y. Fujisawa, T. Kawasaki, Y. Iwasaki, H. Satoh, and K. Shimamoto (2002). The heterotrimeric G protein α subunit acts upstream of the small GTPase rac in disease resistance of rice. Natl. Acad. Sci. USA. 99(20): 13307–13312.
41. Sun, H., Q. Qian, K. Wu, J. Luo, S. Wang, C. Zhang, Y. Ma, Q. Liu, X. Huang, Q. Yuan, R. Han, M. Zhao, G. Dong, L. Guo, X. Zhu, Z. Gou, W. Wang, Y. Wu, H. Lin, and X. Fu (2014). Heterotrimeric G proteins regulate nitrogen-use efficiency in rice. Nat. Genet. 46(6): 652–656.
42. Sun, S., L. Wang, H. Mao, L. Shao, X. Li, J. Xiao, Y. Ouyang, and Q. Zhang (2018). A G-protein pathway determines grain size in rice. Nat. Commun. 9: 851.
43. Tanaka, A., H. Nakagawa, C. Tomita, Z. Shimatani, M. Ohtake, T. Nomura, C. J. Jiang, J. G. Dubouzet, S. Kikuchi, H. Sekimoto, T. Yokota, T. Asami, T. Kamakura, and M. Mori (2009). BRASSINOSTEROID UPREGULATED1, encoding a helix-loop-helix protein, is a novel gene involved in brassinosteroid signaling and controls bending of the lamina joint in rice. Plant Physiol. 151(2):669–680.
44. Temple, B. R. S., and A. M. Jones (2007).The plant heterotrimeric G-Protein complex. Rev. Plant Biol. 58: 249–266.
45. Tong, H., Y. Xiao, D. Liu, S. Gao, L. Liu, Y. Yin, Y. Jin, Q. Qian, and C. Chu (2014). Brassinosteroid regulates cell elongation by modulating gibberellin metabolism in rice. Plant Cell. 26(11): 4376–4393.
46. Ueguchi-Tanaka, M., Fujisawa, M. Kobayashi, M. Ashikari, Y. Iwasaki, H. Kitano, and M. Matsuoka (2000). Rice dwarf mutant d1, which is defective in the α subunit of the heterotrimeric G protein, affects gibberellin signal transduction. Proc. Natl. Acad. Sci. USA. 97(21): 11638–11643.
47. Ueguchi-Tanaka, M., M. Ashikari, M. Nakajima, H. Itoh, E. Katoh, M. Kobayashi, T. Y. Chow, Y. I. C. Hsing, H. Kitano, I. Yamaguchi, and M. Matsuoka (2005). GIBBERELLIN INSENSITIVE DWARF1 encodes a soluble receptor for gibberellin. Nature. 437(7059): 693–698.
48. Ullah, H., J. G. Chen, J. C. Young, K. H. Im, M. R. Sussman, and A. M. Jones (2001). Modulation of cell proliferation by heterotrimeric G protein in Arabidopsis. Science. 292(5524): 2066–2069.
49. Urano, D., J. G. Chen, J. R. Botella, and A. M. Jones (2013). Heterotrimeric G protein signalling in the plant kingdom. Open Biol. 3(3): 120186.
50. Urano, D., A. Colaneri, and A. M. Jones (2014). Gα modulates salt-induced cellular senescence and cell division in rice and maize. J. Exp. Bot. 65(22): 6553–6561.
51. Urano, D., K. Miura, Q. Wu, Y. Iwasaki, D. Jackson, and A. M. Jones (2016). Plant morphology of heterotrimeric G protein mutants. Plant Cell Physiol. 57(3): 437–445.
52. Wang, L., Y. Xu,, Q. Ma, D. Li,, Z. Xu, and K. Chong (2006). Heterotrimeric G protein α subunit is involved in rice brassinosteroid response. Cell Res. 16: 916–922.
53. Wang, Y., Y. Wang, and D. Deng (2019). Multifaceted plant G protein: interaction network, agronomic potential, and beyond. Planta. 249: 1259–1266.
54. Wei, X., S. Tang, G. Shao, M. Chen, Y. Hu, and P. Hu (2013). Fine mapping and characterization of a novel dwarf and narrow-leaf mutant dnl1 in rice. Genet. Mol. Res. 12(3): 3845–3855.
55. Yadav, D. K., D. Shukla, and N. Tuteja (2013). Rice heterotrimeric G-protein α subunit (RGA1): In silico analysis of the gene and promoter and its upregulation under abiotic stress. Plant Physiol. Biochem. 63: 262–271.
56. Yang, D., X. Zheng, C. Cheng, W. Wang, D. Xing, L. Lu, C. Liu, N. Ye, M. Zeng, and X. Ye (2014). A dwarfing mutant caused by deactivation function of α subunit of the heterotrimeric G-protein in rice. Euphytica. 197(1): 145–159.
57. Yang, Y., J. Xiong, L. Tao, Z. Cao, W. Tang, J. Zhang, X. Yu, G. Fu, X. Zhang, and Y. Lu (2020). Regulatory mechanisms of nitrogen (N) on cadmium (Cd) uptake and accumulation in plants: A review. Sci. Total Environ. 708: 135186.
58. Zhang, C., M. Bai, and K. Chong (2014). Brassinosteroid-mediated regulation of agronomic traits in rice. Plant Cell Rep. 33(5): 683–696.
59. Zhang, Y., Y. Zhu, Y. Peng, D. Yan, Q. Li, J. Wang, L. Wang, and Z. He (2008). Gibberellin homeostasis and plant height control by EUI and a role for gibberellin in root gravity responses in rice. Cell Res. 18(3): 412–421.
60. Zhuang, J., H. Lin, J. Lu, H. Qian, S. Hittalmani, N. Huang, and K. Zheng (1997). Analysis of QTL×environment interaction for yield components and plant height in rice. Appl. Genet. 95(5–6): 799–808.