The tomato WRKY-B transcription factor modulates lateral branching by targeting <i>BLIND</i>, <i>PIN4</i>, and <i>IAA15</i>

Abstract

Lateral branching is a crucial agronomic trait that impacts crop yield. In tomato ( <b><i>Solanum lycopersicum</i></b> ), excessive lateral branching is unfavorable and results in substantial labor and management costs. Therefore, optimizing lateral branching is a primary objective in tomato breeding. Although many genes related to lateral branching have been reported in tomato, the molecular mechanism underlying their network remains elusive. In this study, we found that the expression profile of a <i>WRKY</i> gene, <i>WRKY-B</i> (for <i>WRKY-BRANCING</i>), was associated with the auxin-dependent axillary bud development process. <i>Wrky-b</i> mutants generated by the CRISPR/Cas9 editing system presented fewer lateral branches, while <i>WRKY-B</i> overexpression lines presented more lateral branches than did wild-type plants. Furthermore, WRKY-B can directly target the well-known branching gene <i>BLIND</i> (<i>BL</i>) and the auxin efflux carrier gene <i>PIN4</i> to activate their expression. Both the <i>bl</i> and <i>pin4</i> mutants exhibited reduced lateral branching, similar to the <i>wrky-b</i> mutant. The IAA contents in the axillary buds of the <i>wrky-b</i>, <i>bl</i>, and <i>pin4</i> mutant plants were significantly higher than those in the wild-type plants. In addition, WRKY-B can also directly target the AUX/IAA gene <i>IAA15</i> and repress its expression. In summary, <i>WRKY-B</i> works upstream of <i>BL</i>, <i>PIN4</i>, and <i>IAA15</i> to regulate the development of lateral branches in tomato.