Hairs absent is Involved in Type I Trichome Initiation in Tomato

Abstract

Trichomes are specialized epidermal structures and can be categorized into two types: glandular and non-glandular trichomes. Trichomes play an important role in plant defense against biotic and abiotic stresses by serving as physical barriers or chemical factories. Arabidopsis has one type of unicellular trichomes, while tomato has seven types of multicellular trichomes. In the Rosids including Arabidopsis, the initiation pathway of trichomes has been well studied. However, in the Asterids including tomato, only a few genes related to trichome development were identified so far. To identify genes involved in trichome initiation of tomato, we characterized the tomato trichome mutant, hairs absent (h), which does not have the longest glandular trichomes (type I) on stems and sepals. Using a map-based cloning, we identified that H encodes a zinc finger protein homologous to Arabidopsis GLABROUS INFLORESCENCE STEMS, which is a key regulator in trichome development on inflorescence stems. The h mutation showed whole deletion of Solyc10g078970 gene. In addition, we identified additional h mutation alleles from wild species of tomato, S. pimpinellifolium and S. pennellii, both of which also do not have type I trichomes. These results indicate that Solyc10g078970 is H gene. By developing knock-out mutant of Solyc10g078990 gene, which is the closest homolog of Solyc10g078970, using the CRISPR-Cas9 system, we revealed that Solyc10g078990 was involved in trichome development of leaves in tomato. RNA-seq comparison between wild-type and h mutant showed that 1570 genes were differentially regulated by H gene. These genes will be further studied for the identification of new trichome developmental genes and secondary metabolite biosynthetic genes.