SlHDZIV3 and SlHDZIV9 Are Two Positive Regulators in the Formation of Tomato Trichomes.

Trichomes serve as the first line of defense for plants against biotic and abiotic stress. The HD-ZIP IV family plays conserved roles in regulating the development of trichomes in different species, but its specific regulatory mechanism in tomato is not fully understood. In this study, we demonstrate that SlHDZIV3 and SlHDZIV9 are positive regulators of trichome development in tomato, and they function in a partially redundant yet distinct manner. SlHDZIV3 primarily affects the formation of long trichomes on tomato leaves and early formed leaf petiole, while SlHDZIV9 influence the formation of long trichomes across a broader range of tissues, including the fruit trichomes. The CRISPR/Cas9 mutants of SlHDZIV9 exhibit a reduction in fruit trichomes, leading to an extended postharvest shelf-life of tomato fruit. In addition, both SlHDZIV3 and SlHDZIV9 are essential for jasmonic acid-mediated regulation of long trichomes formation. This study enhances our understanding of trichome initiation and development in tomato and provides new strategies for improving postharvest preservation of tomato fruits.