DLT/OsGRAS-32, regulating leaf width and thickness by controlling cell number in Oryza sativa

The improvement of rice leaf morphology is an important goal of rice plant breeding. Studying its molecular development mechanism will facilitate the breeding of a maximally efficient plant type. To further study the developmental mechanism of rice leaves, a dwarf broad-leaf mutant, g44, was obtained by ethyl methanesulfonate mutagenesis of the rice restorer line Jinhui10, and genetic analysis indicated that the trait was controlled by a pair of recessive nuclear gene. The locus was fine mapped on chromosome 6 with 16-kb physical distance. Sequencing revealed that an A-T base substitution occurred in the mutant, resulting in the early termination of LOC_Os06g03710/DLT translation in g44 and yielding only one residual peptide containing 558 amino acids. The phenotypic and sequencing results of the complementary transgenic plants and the allelic mutant g44-1 further confirmed this result. Mutant plants grown under field conditions showed dwarfing, a leaf colour of dark green, leaf widening, and grain enlargement. Paraffin section and cryosection analysis showed that the increase in the number of large vascular bundles and small vascular bundles and the increase in the spacing between adjacent small vascular bundles were the main reasons for the broadening of mutant leaves. In addition, the increase in thickness of the mesophyll cell layer may be the main reason for the increase in leaf colour darkness and net photosynthetic rate. The qPCR results preliminarily predicted that the increase in the number of mutant cells was caused by an enhanced cell division ability, and the DLT/G44 gene was proposed to participate in the regulation of cell division by suppressing the expression of cyclin-related genes.