Department of Soil and Crop Sciences, Texas A&M University and Texas A&M AgriLife Research, College Station, Texas 77843.
Plant Physiol. 2013 Oct;163(2):1047-58. doi: 10.1104/pp.113.221895. Epub 2013 Aug 8.
Low red light/far-red light ratio (R:FR) serves as an indicator of impending competition and has been demonstrated to suppress branch development. The regulation of Arabidopsis (Arabidopsis thaliana) rosette bud outgrowth by the R:FR and the associated mechanisms were investigated at several levels. Growth under low R:FR suppressed outgrowth of the third from topmost bud (bud n-2) but not that of the topmost bud. Subsequently increasing the R:FR near the time of anthesis promoted bud n-2 outgrowth and reduced topmost bud growth. Buds from specific rosette positions, exhibiting divergent fates to increased R:FR, were harvested 3 h after modifying the R:FR and were used to conduct ATH1 microarray-based transcriptome profiling. Differentially expressed genes showed enrichment of light signaling and hormone-related Gene Ontology terms and promoter motifs, most notably those associated with abscisic acid (ABA). Genes associated with ABA biosynthesis, including the key biosynthetic gene NINE-CIS-EPOXYCAROTENOID DIOXYGENASE3 (NCED3), and with ABA signaling were expressed at higher levels in the responsive bud n-2, and increasing the R:FR decreased their expression only in bud n-2. ABA abundance in responsive buds decreased within 12 h of increasing the R:FR, while indole-3-acetic acid levels did not change. A role for ABA in repressing bud outgrowth from lower positions under low R:FR was demonstrated using the nced3-2 and aba2-1 ABA biosynthesis mutants, which showed enhanced branching and a defective bud n-2 outgrowth response to low R:FR. The results provide evidence that ABA regulates bud outgrowth responses to the R:FR and thus extend the known hormonal pathways associated with the regulation of branching and shade avoidance.
低红光/远红光比值（R:FR）可作为即将发生竞争的指标，已被证明可抑制分枝发育。在多个水平上研究了 R:FR 对拟南芥（Arabidopsis thaliana）莲座丛芽生长的调控及其相关机制。在低 R:FR 下生长会抑制最上面第三芽（芽 n-2）的生长，但不会抑制最上面芽的生长。随后，在花期附近增加 R:FR 会促进芽 n-2 的生长，并减少最上面芽的生长。从特定的莲座丛位置收获具有不同命运的芽，这些芽对增加的 R:FR 做出反应，在改变 R:FR 后 3 小时收获，并用于进行 ATH1 基于微阵列的转录组谱分析。差异表达基因显示出光信号和激素相关的基因本体论术语和启动子基序的富集，特别是那些与脱落酸（ABA）相关的术语和基序。与 ABA 生物合成相关的基因，包括关键生物合成基因 NINE-CIS-EPOXYCAROTENOID DIOXYGENASE3（NCED3），以及与 ABA 信号转导相关的基因，在响应芽 n-2 中表达水平更高，并且增加 R:FR 仅降低芽 n-2 中的表达。在增加 R:FR 后 12 小时内，响应芽中 ABA 的丰度下降，而吲哚-3-乙酸的水平没有变化。使用 nced3-2 和 aba2-1 ABA 生物合成突变体证明了 ABA 在低 R:FR 下抑制较低位置芽生长的作用，这些突变体表现出增强的分枝和对低 R:FR 的芽 n-2 生长反应缺陷。结果提供了证据表明 ABA 调节芽对 R:FR 的生长反应，从而扩展了与分枝和避荫调节相关的已知激素途径。
