Abstract
Unlike many wild grasses, domesticated rice cultivars have uniform culm height and panicle size among tillers and the main shoot, which is an important trait for grain yield. However, the genetic basis of this trait remains unknown. Here, we report that DWARF TILLER1 (DWT1) controls the developmental uniformity of the main shoot and tillers in rice (Oryza sativa). Most dwt1 mutant plants develop main shoots with normal height and larger panicles, but dwarf tillers bearing smaller panicles compared with those of the wild type. In addition, dwt1 tillers have shorter internodes with fewer and un-elongated cells compared with the wild type, indicating that DWT1 affects cell division and cell elongation. Map-based cloning revealed that DWT1 encodes a WUSCHEL-related homeobox (WOX) transcription factor homologous to the Arabidopsis WOX8 and WOX9. The DWT1 gene is highly expressed in young panicles, but undetectable in the internodes, suggesting that DWT1 expression is spatially or temporally separated from its effect on the internode growth. Transcriptomic analysis revealed altered expression of genes involved in cell division and cell elongation, cytokinin/gibberellin homeostasis and signaling in dwt1 shorter internodes. Moreover, the non-elongating internodes of dwt1 are insensitive to exogenous gibberellin (GA) treatment, and some of the slender rice1 (slr1) dwt1 double mutant exhibits defective internodes similar to the dwt1 single mutant, suggesting that the DWT1 activity in the internode elongation is directly or indirectly associated with GA signaling. This study reveals a genetic pathway synchronizing the development of tillers and the main shoot, and a new function of WOX genes in balancing branch growth in rice.
Highlights
Rice is one of the most important crops in the world and feeds more than half of the world population
We identified DWARF TILLER1, a WUSCHEL-related homeobox (WOX) transcription factor, as a positive regulator of tiller growth
Genome-wide expression analysis revealed that the expression of genes related to cell division and elongation, as well as to homeostasis and signaling of cytokinin and gibberellin were affected in dwt1 un-elongated internodes
Summary
Rice is one of the most important crops in the world and feeds more than half of the world population. A mature rice plant has a main shoot and several lateral branches (tillers), with each bearing an inflorescence (panicle) at the apex. Despite their differences in bud initiation time, the main shoot and all tillers grow to a uniform height and flower at the same time [1]. The uniform growth of tillers and the main shoot in many cultivated cereal crops, such as rice, wheat, barley, is an important agricultural trait because it ensures uniform grain size, and synchronized maturation time and a uniform panicle layer which facilitates harvesting [2]. The genetic basis underlying the uniform development of tillers and the main shoot in these crops remains unknown
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