• Plant hormones can adjust the physiology and development of plants to enhance their adaptation to biotic and abiotic challenges. Jasmonic acid (JA), one of the immunity hormones in plants, triggers genome‐wide transcriptional changes in response to insect attack and wounding. Although JA is known to affect the development of trichomes, epidermal appendages that form a protective barrier against various stresses, it remains unclear how JA interacts with developmental programs that regulate trichome development.
• In this study, we show that JA affects trichome length in tomato by releasing the transcriptional repression mediated by Jasmonate ZIM (JAZ) proteins. We identified SlJAZ4, a negative regulator preferentially expressed in trichomes, as the critical component in JA signaling in tomato trichomes.
• We also identified a homeodomain‐leucine zipper gene, SlHD8, as the downstream regulator of JA signaling that promotes trichome elongation. SlHD8 is also highly expressed in trichomes and physically interacts with SlJAZ4. Loss‐of‐function mutations in SlHD8 caused shorter trichomes, a phenotype that was only partially rescued by methyl jasmonate treatment.
• Our dual‐luciferase and chromatin immunoprecipitation–quantitative PCR assays revealed that SlHD8 regulates trichome elongation by directly binding to the promoters of a set of cell‐wall‐loosening protein genes and activating their transcription. Together, our findings define SlHD8‐SlJAZ4 as a key module mediating JA‐induced trichome elongation in tomato.

中文翻译：

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HOMEODOMAIN PROTEIN8介导茉莉酸酯触发的番茄毛状体伸长

• 植物激素可以调节植物的生理和发育，以增强其对生物和非生物挑战的适应性。茉莉酸（JA）是植物中的一种免疫激素，可触发全基因组转录变化，以响应昆虫的攻击和伤害。尽管已知JA影响毛状体的形成，而表皮附肢形成了抵抗各种压力的保护性屏障，但尚不清楚JA如何与调节毛状体发育的发育程序相互作用。
• 在这项研究中，我们表明JA通过释放由茉莉酸ZIM（JAZ）蛋白质介导的转录抑制作用来影响番茄的毛状体长度。我们鉴定了SlJAZ4（一种在毛线虫中优先表达的负调控因子）是番茄毛线虫JA信号传导中的关键成分。
• 我们还鉴定了同源域亮氨酸拉链基因SlHD8作为促进毛状体伸长的JA信号的下游调节子。SlHD8在毛状体中也高表达，并与SlJAZ4物理相互作用。SlHD8的功能丧失突变导致较短的毛状体，该表型仅通过茉莉酸甲酯处理得以部分挽救。
• 我们的双荧光素酶和染色质免疫沉淀定量PCR分析表明，SlHD8通过直接结合一组细胞壁松弛蛋白基因的启动子并激活其转录来调节毛状体的伸长。总之，我们的发现将SlHD8-SlJAZ4定义为介导JA诱导番茄毛状体伸长的关键模块。