Department of Microbiology and Cell Science, University of Florida, PO Box 110700, Gainesville, FL, 32611, USA.
New Phytol. 2017 May;214(3):1245-1259. doi: 10.1111/nph.14442. Epub 2017 Jan 30.
Although in recent years nonhost resistance has attracted considerable attention for its broad spectrum and durability, the genetic and mechanistic components of nonhost resistance have not been fully understood. We used molecular and histochemical approaches including quantitative PCR, chromatin immunoprecipitation, and 3,3'-diaminobenzidine and aniline blue staining. The evolutionarily conserved histone acetyltransferase complex Elongator was identified as a major component of nonhost resistance against Xanthomonas citri subsp. citri (Xcc) and Pseudomonas syringae pv. phaseolicola (Psp) NPS3121. Mutations in Elongator genes inhibit Xcc-, Psp NPS3121- and/or flg22-induced defense responses including defense gene expression, callose deposition, and reactive oxygen species (ROS) and salicylic acid (SA) accumulation. Mutations in Elongator also attenuate the ROS-SA amplification loop. We show that suppressed ROS and SA accumulation in Elongator mutants is correlated with reduced expression of the Arabidopsis respiratory burst oxidase homologue AtrbohD and the SA biosynthesis gene ISOCHORISMATE SYNTHASE1 (ICS1). Furthermore, we found that the Elongator subunit ELP2 is associated with the chromatin of AtrbohD and ICS1 and is required for maintaining basal histone H3 acetylation levels in these key defense genes. As both AtrbohD and ICS1 contribute to nonhost resistance against Xcc, our results reveal an epigenetic mechanism by which Elongator regulates nonhost resistance in Arabidopsis.
虽然近年来非寄主抗性因其广谱性和持久性而引起了相当大的关注，但非寄主抗性的遗传和机制组成部分尚未得到充分理解。我们使用了包括定量 PCR、染色质免疫沉淀和 3,3'-二氨基联苯胺和苯胺蓝染色在内的分子和组织化学方法。进化上保守的组蛋白乙酰转移酶复合物 Elongator 被鉴定为非寄主抗性针对柑橘溃疡病菌（Xanthomonas citri subsp. citri，Xcc）和丁香假单胞菌 pv. 菜豆致病变种（Pseudomonas syringae pv. phaseolicola，Psp NPS3121）的主要组成部分。Elongator 基因的突变抑制了 Xcc、Psp NPS3121-和/或 flg22 诱导的防御反应，包括防御基因表达、胼胝质沉积以及活性氧（ROS）和水杨酸（SA）的积累。Elongator 基因的突变也减弱了 ROS-SA 放大环。我们表明，Elongator 突变体中 ROS 和 SA 积累的抑制与拟南芥呼吸爆发氧化酶同源物 AtrbohD 和 SA 生物合成基因 ISOCHORISMATE SYNTHASE1（ICS1）的表达减少有关。此外，我们发现 Elongator 亚基 ELP2 与 AtrbohD 和 ICS1 的染色质相关，并且是维持这些关键防御基因中基础组蛋白 H3 乙酰化水平所必需的。由于 AtrbohD 和 ICS1 都有助于对 Xcc 的非寄主抗性，我们的结果揭示了 Elongator 通过表观遗传机制调节拟南芥非寄主抗性的机制。
