Comprehensive observation of trichome development in Micro-tom tomato

Trichomes help plants defend against various stresses by formation of a protective barrier. Although the unicellular trichomes in Arabidopsis have been well studied, little is known of the development of multicellular trichomes in tomato. With seven morphologically and functionally different types, tomato trichomes are more complex than the unicellular trichomes in Arabidopsis. Here, we comprehensively analyzed the spatiotemporal pattern of tomato trichome development. Our observations show that the gradual reduction of type I/IV trichomes during leaf development is accompanied by an increase of other trichome types. We further examined the gland development of type I/IV trichomes by constructing a marker reporter, pSlAT2: GUS-YFP which is specifically expressed in the top cell of the trichomes. Interestingly, we found the multicellular base of trichomes is initiated as early as the two-cell stage. Through tracking a nuclear marker, H2B-GFP in tomato trichomes, we found the correlation between stalk cell length and nuclear size, suggesting that cell ploidy level could affect trichome cell size. Finally, we found type VII glandular trichomes exhibit two morphologically distinct forms, with the majority covered by a wax-like substance, which could help to form extra storage space for secretory metabolites. Our results provide the basis for further mechanistic study of trichome development in tomato.