OsLBD3-7 Overexpression Induced Adaxially Rolled Leaves In Rice

Rice leaf shape or three-dimensional architecture plays important roles in the leaf’s function, including photosynthesis, respiration and transpiration. Appropriate leaf rolling enhances erect-leaf habits and photosynthetic efficiency, which consequently improves grain yield. In contrast, serious leaf rolling could hinder plant development and severely reduce crop yield. Bulliform cells are groups of large and highly vacuolated cells that mainly exist in monocots and play a crucial role in the modulation of leaf rolling. It has been shown that the shrinking or expanding of bulliform cells contribute to the leaf rolling up or opening under different water stress conditions. Here, we reported the novel lateral organ boundaries domain(LBD) gene OsLBD3-7, which is involved in the regulation of leaf rolling. LBD gene family is a plant-specific transcription factor family. LBD proteins contain a characteristic LOB domain composed of a C-motif that is required for DNA-binding, a conserved glycine residue, and a leucine-zipper-like sequence that is required for protein-protein interactions. LBD genes are involved in embryonic shoot apical meristem(SAM) formation and have an important influence on the formation and development of plant lateral organs, such as leaves, flowers and roots. In this study, OsLBD3-7V and OsLBD3-7 overexpression leads to narrow and adaxially rolled leaves. Microscopy of flag leaf cross-sections indicated that overexpression of OsLBD3-7 led to a decrease in both bulliform cell size and number. To investigate the expression pattern of OsLBD3-7, we monitored its expression throughout its life period(from seeding to mature caryopses) with qRT-PCR. Our results showed that OsLBD3-7 was ubiquitously expressed in almost all of the detected tissues, with especially high expression in the sheath and roots. Transient expression in Arabidopsis mesophyll protoplasts showed that OsLBD3-7-YFP was exclusively located on the plasma membrane and in the nucleus. Transactivation activity assays in yeast indicated that both OsLBD3-7 and OsLBD3-7V work as transcription activators. Transcriptional analysis showed that key genes that had been reported to be negative regulators of bulliform cell development were up-regulated in transgenic plants. These results indicated that OsLBD3-7 might acts as an upstream regulatory gene of bulliform cell development to regulate leaf rolling, which will give more insights on the leaf rolling regulation mechanism.