College of Horticulture, Shenyang Agricultural University, Shenyang 110866, China.
Key Laboratory of Protected Horticulture of Ministry of Education, Shenyang 110866, China.
Plant Physiol. 2022 Aug 1;189(4):2396-2412. doi: 10.1093/plphys/kiac212.
Plant organ abscission, a process that is important for development and reproductive success, is inhibited by the phytohormone auxin and promoted by another phytohormone, jasmonic acid (JA). However, the molecular mechanisms underlying the antagonistic effects of auxin and JA in organ abscission are unknown. We identified a tomato (Solanum lycopersicum) class III homeodomain-leucine zipper transcription factor, HOMEOBOX15A (SlHB15A), which was highly expressed in the flower pedicel abscission zone and induced by auxin. Knocking out SlHB15A using clustered regularly interspaced short palindromic repeats-associated protein 9 technology significantly accelerated abscission. In contrast, overexpression of microRNA166-resistant SlHB15A (mSlHB15A) delayed abscission. RNA sequencing and reverse transcription-quantitative PCR analyses showed that knocking out SlHB15A altered the expression of genes related to JA biosynthesis and signaling. Furthermore, functional analysis indicated that SlHB15A regulates abscission by depressing JA-isoleucine (JA-Ile) levels through inhabiting the expression of JASMONATE-RESISTANT1 (SlJAR1), a gene involved in JA-Ile biosynthesis, which could induce abscission-dependent and abscission-independent ethylene signaling. SlHB15A bound directly to the SlJAR1 promoter to silence SlJAR1, thus delaying abscission. We also found that flower removal enhanced JA-Ile content and that application of JA-Ile severely impaired the inhibitory effects of auxin on abscission. These results indicated that SlHB15A mediates the antagonistic effect of auxin and JA-Ile during tomato pedicel abscission, while auxin inhibits abscission through the SlHB15A-SlJAR1 module.
植物器官脱落，一个对发育和生殖成功很重要的过程，受到植物激素生长素的抑制，而受到另一种植物激素茉莉酸（JA）的促进。然而，生长素和 JA 在器官脱落中拮抗作用的分子机制尚不清楚。我们鉴定了一个番茄（Solanum lycopersicum）类 III 同源盒-亮氨酸拉链转录因子，HOMEOBOX15A（SlHB15A），它在花柄脱落区高度表达，并被生长素诱导。使用聚类规则间隔短回文重复相关蛋白 9 技术敲除 SlHB15A 显著加速了脱落。相比之下，过表达微 RNA166 抗性 SlHB15A（mSlHB15A）则延迟了脱落。RNA 测序和反转录定量 PCR 分析表明，敲除 SlHB15A 改变了与 JA 生物合成和信号相关的基因的表达。此外，功能分析表明，SlHB15A 通过抑制参与 JA-Ile 生物合成的基因 JASMONATE-RESISTANT1（SlJAR1）的表达来调节脱落，从而降低 JA-Ile 水平，这可以诱导依赖于脱落和不依赖于脱落的乙烯信号。SlHB15A 直接结合到 SlJAR1 启动子上沉默 SlJAR1，从而延迟脱落。我们还发现，去除花朵会增加 JA-Ile 的含量，而施加 JA-Ile 会严重损害生长素对脱落的抑制作用。这些结果表明，SlHB15A 在番茄花柄脱落过程中介导生长素和 JA-Ile 的拮抗作用，而生长素通过 SlHB15A-SlJAR1 模块抑制脱落。
