CsBRC1 inhibits axillary bud outgrowth by directly repressing the auxin efflux carrier CsPIN3 in cucumber

First author: Junjun Shen; Affiliations: China Agricultural University (中国农业大学): Beijing, China

Corresponding author: Xiaolan Zhang

Shoot branching is an important agronomic trait that directly determines plant architecture and affects crop productivity. To promote crop yield and quality, axillary branches need to be manually removed during cucumber production for fresh market and thus are undesirable. Auxin is well known as the primary signal imposing for apical dominance and acts as a repressor for lateral bud outgrowth indirectly. The TEOSINTE BRANCHED1/CYCLOIDEA/PCF (TCP) family gene BRANCHED1 (BRC1) has been shown to be the central integrator for multiple environmental and developmental factors that functions locally to inhibit shoot branching. However, the direct molecular link between auxin and BRC1 remains elusive. Here we find that cucumber BRANCHED1 (CsBRC1) is expressed in axillary buds and displays a higher expression level in cultivated cucumber than in its wild ancestor. Knockdown of CsBRC1 by RNAi leads to increased bud outgrowth and reduced auxin accumulation in buds. We further show that CsBRC1 directly binds to the auxin efflux carrier PIN-FORMED (CsPIN3) and negatively regulates its expression in vitro and in vivo. Elevated expression of CsPIN3 driven by the CsBRC1 promoter results in highly branched cucumber with decreased auxin levels in lateral buds. Therefore, our data suggest that CsBRC1 inhibits lateral bud outgrowth by direct suppression of CsPIN3 functioning and thus auxin accumulation in axillary buds in cucumber, providing a strategy to breed for cultivars with varying degrees of shoot branching grown in different cucumber production systems.

茎分枝是一个非常重要的农艺性状，直接决定了植物的株型，并且影响作物的产量。为了促进作物产量和质量，在黄瓜结果时需要人工去除腋分枝。生长素是植物顶端优势中主要的信号，能够间接抑制侧芽的向外生长。已知TCP基因家族的基因BRC1是多个环境和发育因素的中央调控因子，作用于区域性的茎分枝抑制。然而，生长素与BRC1蛋白之间直接的联系还不清楚。本文中，作者发现黄瓜中CsBRC1基因在腋生芽中表达，并且相比于其野生种，栽培种黄瓜腋生芽中的CsBRC1基因表达量更高。通过RNAi技术敲低CsBRC1基因的表达会增加芽的生长，并降低生长素在芽中的积累。进一步的研究显示CsBRC1能够直接结合到生长素运输基因CsPIN3上，并且在体内外条件下均能够负调控CsPIN3基因的表达。通过CsBRC1的启动子提升CsPIN3的表达能够导致黄瓜高度分枝，并且侧芽中生长素的积累降低。因此，本文的研究显示黄瓜中CsBRC1蛋白通过直接抑制CsPIN3基因的表达，从而降低腋芽中生长素的积累，进而抑制侧芽的向外生长。作者的研究为栽培种黄瓜的育种提供了一个新的策略，用于在不同的黄瓜生产系统中调控黄瓜植株的分枝程度。

通讯：张小兰  (http://yyxy.cau.edu.cn/art/2018/2/18/art_29675_28.html)

个人简介：1995-1999年，中国农业大学，学士；1999-2002年，中国农业大学，硕士；2002-2007年，美国佐治亚大学，博士；2007- 2011年，美国加州理工大学，博士后。

研究方向：蔬菜花和果实发育的分子机理；黄瓜性别决定的分子机制；黄瓜果刺的起始与膨大的基因调控网络。

doi: https://doi.org/10.1073/pnas.1907968116

Journal: PNAS

Published date: August 07, 2019

张老师往期精彩：

New Phytologist：黄瓜CsLFY基因作用于茎尖分生维持  http://blog.sciencenet.cn/home.php?mod=space&uid=3158122&do=blog&quickforward=1&id=1091479

the plant journal：黄瓜CsSPL基因作用于花药和胚珠的生长发育  http://blog.sciencenet.cn/home.php?mod=space&uid=3158122&do=blog&id=1106769

Plant Cell：黄瓜果实长度的分子调控机制  http://blog.sciencenet.cn/blog-3158122-1173225.html