Functional Verification Of ZmGRF10Gene And Evaluation Of New Breeding Materials In Maize (Zea Mays L.)

It has long been thought that growth-regulating factors (GRF) gene family members act as transcription factors to play important roles in multiple plant developmental processes. However, the recent characterization of Arabidopsis GRF7showed that it functions as a transcriptional repressor of osmotic stress-responsive genes. This highlights the complex and diverse mechanisms by which different GRF members employ to take action,in this study, the maize GRF10was functionally characterized to improve this concept.Previously, we have cloned14GRFs and3GIFs genes from maize, and compared their tissue-specific expression patterns. Only two GRF members, ZmGRFl and ZmGRF10, are highly expressed in immature leaves and shoot. Initial transgenic transformation of these two genes in Arabidopsis revealed, to our surprise, the overexpression of ZmGRF10, not ZmGRFl, exhibited phenotype with reduced leaf size. The deduced ZmGRF10protein retains the N-terminal QLQ and WRC domains, the characteristic regions as protein-interacting and DNA binding domains, respectively. However it lacks nearly the entire C-terminal domain, the regions executing transactivation activity. Consistently, ZmGRF10protein maintains the ability to interact with GIFs proteins, but lacks transactivation activity.To understand the significance of increased expression of ZmGRF10, the full-length ZmGRF10cDNA was ectopically expressed in maize driven by CaMV35S promoter. Transformed maize lines in the original Hi-II background were characterized by Southern blot analysis and two independent transgenic lines were identified. Subsequently, these two transgenic events were integrated into Zheng58, an elite Chinese inbred line, through repeated-backcrossing for7times under the PCR-marker-assisted selection.The phenotypic characterization and statistical analysis of genetically modified (gm) near isogenic line show that overexpression of ZmGRF10in maize led to a reduction in leaf size and plant height through decreasing cell proliferation, whereas the yield-related traits were not affected. The resultant phenotypes caused by the over-expression of ZmGRF10were persistent in hybrid.Transcriptome analysis revealed that multiple biological pathways were affected by ZmGRF10overexpression, including a few of transcriptional regulatory genes which have been demonstrated to have important roles in controlling plant growth and development. We propose that ZmGRF10aids in fine-tuning the homeostasis of the GRF-GIF complex in the regulation of cell proliferation.