Genome-wide analysis of RopGEF gene family to identify genes contributing to pollen tube growth in rice (Oryza sativa)

Abstract

Background: In plants, the key roles played by RopGEF-mediated ROP signaling in diverse processes, including polar tip growth, have been identified. Despite their important roles in reproduction, a comprehensive analysis of RopGEF members has not yet been performed in rice (Oryza sativa). To determine whether RopGEF regulators are involved in rice pollen tube growth, we performed genome-wide analysis of this family in rice. Results: Phylogenomic and meta-expression analysis of eleven RopGEFs in rice showed that four genes were preferentially expressed in mature pollen. These four genes contain the plant-specific Rop nucleotide exchanger (PRONE) domain and possible phosphorylated residues, suggesting a conserved role in polar tip growth with Arabidopsis thaliana. In subcellular localization analysis of the four RopGEFs through tobacco (Nicotiana benthamiana) infiltration, four proteins were predominantly identified in plasma membrane. Moreover, double mutants of RopGEF2/8 exhibited reduced pollen germination, causing partial male sterility. These genes possess unique cis-acting elements in their promoters compared with the other RopGEF genes. Conclusions: In this study, four RopGEF genes were identified as pollen-specific gene in eleven members of rice, and the expression pattern, promoter analysis, and evolutionary relationship of the RopGEF family were studied compared with Arabidopsis. Our study indicated that four RopGEF genes might function during pollen germination in distinct subcellular localization. Our study could provide valuable information on the functional study of RopGEF in rice.

GORI, encoding the WD40 domain protein, is required for pollen tube germination and elongation in rice

“…Arabidopsis encodes three pollen‐specific ROP genes ( ROP1 , ROP3 and ROP5 ), and ROP1 is a central regulator of polar PT growth via regulation of F‐actin dynamics and apical exocytosis (Gu et al ., 2003; Luo et al ., 2017). Recently, we found that rice has one ROP gene showing a high expression level in pollen, namely Rac6 , which is also ubiquitously expressed in other rice tissues (Kim et al ., 2020a). The difference in the expression patterns of ROP genes between the two species may cause distinct regulation by REN4 and GORI.…”

“…The rupo PTs also burst precociously in vivo and in vitro (Liu et al, 2016), suggesting that conserved mechanisms of RLK-mediated signaling are involved in the cell wall integrity of PTs. Recently, we identified four pollen-specific Rop-GEF genes in rice; the RopGEF2/-8 double mutant exhibited partial sterility owing to a reduced pollen germination ratio (Kim et al, 2020a) whereas the single mutant exhibited no significant difference in fertility. Similarly, Arabidopsis showed a PT defect in the quadruple mutants, suggesting their redundant ROP regulatory function (Chang et al, 2013).…”

Signalling Pinpointed to the Tip: The Complex Regulatory Network That Allows Pollen Tube Growth

“…RopGEFs were then proposed as integration points for guidance cues, as an increased activation of Rop1 in response to a guidance cue would cause the shift in Rop1 activity and re-direction of secretion [ 12 ]. Consequently, RopGEFs, RhoGAPs, and RhoGDIs are important modulators of pollen tube growth due to their regulation of Rop/Rac GTPases [ 124 , 136 , 148 , 149 , 150 ]. Thus, male transmission defects were observed when RhoGDI function was missing in Arabidopsis [ 149 ].…”

Interaction of OsRopGEF3 Protein With OsRac3 to Regulate Root Hair Elongation and Reactive Oxygen Species Formation in Rice (Oryza sativa)

“…The molecular function of RopGEF and ROP/Rac in root hair growth of other plants is less known. There are 11 OsRopGEFs and 7 OsRac genes in rice (Miki et al, 2005;Kim et al, 2020). The functions of control grain size, RNA silencing, apoptosis regulation, and gene expression in OsRacs have been studied (Kawasaki et al, 1999;Miki and Shimamoto, 2004;Zhang et al, 2019).…”

“…The functions of control grain size, RNA silencing, apoptosis regulation, and gene expression in OsRacs have been studied (Kawasaki et al, 1999;Miki and Shimamoto, 2004;Zhang et al, 2019). Phylogenetic analysis and expression profiles suggest different features of ROP between Arabidopsis and rice (Kim et al, 2020). However, it has not been elucidated how OsRopGEF and OsRac regulate root hair development in rice, a model crop plant.…”