Phenotypic Characterization, Fine Mapping, and Altered Expression Profiling of Roses1 Mutation That Affects Organ Size and Water Loss Through Regulating Stomatal Density in Rice

Organ size is an important agronomic trait that directly affects the biomass of rice (Oryza sativa L.), thus identification and characterization of genes involved in organ size control would contribute to basic biology, as well as provide target genes for genetic manipulation of rice yield potential. Although organism or organ size is of pivotal importance, the molecular and genetic mechanisms underlying it remain far from understood. Here we report the isolation and characterization of reduced organ size with early senescence1 (roses1) mutant in rice. The roses1 mutant was obtained by ethyl methanesulfonate mutagenesis, and genetic analysis revealed that roses1 mutation is controlled by a single recessive nuclear gene. Distinct reduction in the size of organs in roses1 mutant plants was attributed to decreased cell number and cell size detected by histological analysis and the early leaf senescence with green and pale brown stripes, probably due to elevated stomata density detected by microscopy analysis. The ROSES1 gene was isolated by using map‐based cloning strategy, encoding a BEL1‐like homeobox transcription factor containing a plant‐specific peroxidase (POX) domain of unknown function. The β‐glucuronidase (GUS) activity driven by the ROSES1 promoter was strongly detected at the root meristem and elongation zone, shoot meristem, node, intercalary meristem of internode, leaf, inflorescence branch, and developing caryopsis and embryo. Differential gene expression analysis revealed potential regulatory networks involved in organ size control and stomata functioning that could be affected by the expression of the ROSES1 protein.