Department of Chemistry, Seoul National University, Seoul 151-742, Korea.
Plant Cell. 2011 Mar;23(3):1138-52. doi: 10.1105/tpc.111.083485. Epub 2011 Mar 11.
Drought stress activates several defense responses in plants, such as stomatal closure, maintenance of root water uptake, and synthesis of osmoprotectants. Accumulating evidence suggests that deposition of cuticular waxes is also associated with plant responses to cellular dehydration. Yet, how cuticular wax biosynthesis is regulated in response to drought is unknown. We have recently reported that an Arabidopsis thaliana abscisic acid (ABA)-responsive R2R3-type MYB transcription factor, MYB96, promotes drought resistance. Here, we show that transcriptional activation of cuticular wax biosynthesis by MYB96 contributes to drought resistance. Microarray assays showed that a group of wax biosynthetic genes is upregulated in the activation-tagged myb96-1D mutant but downregulated in the MYB96-deficient myb96-1 mutant. Cuticular wax accumulation was altered accordingly in the mutants. In addition, activation of cuticular wax biosynthesis by drought and ABA requires MYB96. By contrast, biosynthesis of cutin monomers was only marginally affected in the mutants. Notably, the MYB96 protein acts as a transcriptional activator of genes encoding very-long-chain fatty acid-condensing enzymes involved in cuticular wax biosynthesis by directly binding to conserved sequence motifs present in the gene promoters. These results demonstrate that ABA-mediated MYB96 activation of cuticular wax biosynthesis serves as a drought resistance mechanism.
干旱胁迫会激活植物的几种防御反应，如关闭气孔、维持根系水分吸收和合成渗透保护剂。越来越多的证据表明，角质层蜡的沉积也与植物对细胞脱水的反应有关。然而，角质层生物合成如何响应干旱而受到调节尚不清楚。我们最近报道称，拟南芥脱落酸（ABA）响应的 R2R3 型 MYB 转录因子 MYB96 促进抗旱性。在这里，我们表明 MYB96 通过转录激活角质层生物合成有助于抗旱性。微阵列分析显示，一组蜡生物合成基因在激活标记的 myb96-1D 突变体中上调，但在 MYB96 缺失的 myb96-1 突变体中下调。突变体中的角质层蜡积累相应地发生了改变。此外，干旱和 ABA 对角质层生物合成的激活需要 MYB96。相比之下，突变体中角质的单体生物合成仅受到轻微影响。值得注意的是，MYB96 蛋白作为角质层生物合成中涉及非常长链脂肪酸缩合酶的基因的转录激活因子发挥作用，通过直接结合基因启动子中存在的保守序列基序。这些结果表明，ABA 介导的 MYB96 激活角质层生物合成是一种抗旱机制。
