Screening And Functional Characterization Of The Proteins Interacting With QPE9-1, A Major Gene For Panicle Erectness In Rice

The development and application of panicle erectness (PE) varieties is considered as the third breakthrough in the history of rice breeding in China. One key quantitative trait gene for PE, qPE9-1/DEP1, encoding a novel y subunit of heterotrimeric G protein (G protein), was isolated using a map-based cloning strategy. More reports showed that qPE9-1 not only involved in the regulation of plant architecture and panicle shape, but also controls nitrogen and stress responses. However, the mechanism of how qPE9-1 modifies plant and panicle development and physiological responses remains unknown. So, it is necessary to further reveal the molecular function and genetic regulatory network of qPE9-1.In this study, we obtained two proteins interacting with qPE9-1 using yeast two-hybrid strategy. And the transgenic lines were generated to investigate the biological function of these genes. The main results are as follows:1. Two candidate proteins interacting with qPE9-1, OsSRFP1 and GASR9, were obtained and confirmed through yeast two-hybrid system. OsSRFP1 is an E3 ubiquitin ligase, while GASR9 is encoded by a gibberellic acid-stimulated transcript in rice.2. Sequence analysis showed that there are eleven member of the GASR family in rice genome.Amino acid sequence of GASR9 shows the highest identity (73%) with GRMZM2G077845 in maize. All the family genes in rice, maize and Arabidopsis have conserved C-terminal regions, which contain 12 Cys residues.3. The expression pattern of GASR9 gene was analyzed using real-time PCR. GASR9 constitutively expresses in all plant tissues, including stem, leaf, node, panicle, sheath and root. The highest transcripts were detected in young panicles, while the lowest were examined in roots. The expression level of GASR9 was induced by GA, and declined with the development of panicles. At the same time, the expression level of GASR9 was inhibited by BR and IAA. Subcellular localization indicated that GASR9 protein is localized at plasma membrane, cytoplasm and nucleus.4. To investigate the biological function of GASR9 gene, RNAi and overexpression transgenic lines were generated. The plants with significantly reduced GASR9 transcript exhibited dwarfism, while the individuals with enhanced expression level showed higher plant height. Tissue dissection analysis further revealed that the short internodes resulted from shorten cell length but not cell number. These data suggested that GASR9 gene regulates plant height through cell elongation in rice.