DWARF TILLER1, a WUSCHEL-Related Homeobox Transcription Factor, Is Required for Tiller Growth in Rice

Abstract

<div><p>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 <i>DWARF TILLER1</i> (<i>DWT1</i>) controls the developmental uniformity of the main shoot and tillers in rice (<i>Oryza sativa</i>). Most <i>dwt1</i> 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, <i>dwt1</i> 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 <i>DWT1</i> encodes a WUSCHEL-related homeobox (WOX) transcription factor homologous to the <i>Arabidopsis</i> WOX8 and WOX9. The <i>DWT1</i> gene is highly expressed in young panicles, but undetectable in the internodes, suggesting that <i>DWT1</i> 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 <i>dwt1</i> shorter internodes. Moreover, the non-elongating internodes of <i>dwt1</i> are insensitive to exogenous gibberellin (GA) treatment, and some of the <i>slender rice1</i> (<i>slr1</i>) <i>dwt1</i> double mutant exhibits defective internodes similar to the <i>dwt1</i> 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 <i>WOX</i> genes in balancing branch growth in rice.</p></div