Tomato ARPC1 regulates trichome morphology and density and terpene biosynthesis.

MAIN CONCLUSION: Based on transcriptomic analysis of wild-type and mutant tomato plants, ARPC1 was found to be important for trichome formation and development and it plays a key role in terpene synthesis. Trichomes are protruding epidermal cells in plant species. They function as the first defense layer against biotic and abiotic stresses. Despite the essential role of tomato trichomes in defense against herbivores, the understanding of their development is still incomplete. Therefore, the aim of this study was to identify genes involved in trichome formation and morphology and terpene synthesis, using transcriptomic techniques. To achieve this, we examined leaf morphology and compared the expression levels of some putative genes involved in trichome formation between wild-type (WT) and hairless-3 (hl-3) tomato mutant. The hl-3 plants displayed swollen and distorted trichomes and reduced trichome density (type I and IV) and terpene synthesis compared with that of the WT plants. Gene expression analysis showed that Actin-Related Protein Component1 (ARPC1) was expressed more highly in the WT than in the hl-3 mutant, indicating its critical role in trichome morphology and density. Additionally, the expression of MYC1 and several terpene synthase genes (TPS9, 12, 20), which are involved in type VI trichome initiation and terpene synthesis, was lower in the hl-3 mutant than in the WT plants. Moreover, transformation of the hl-3 mutant with WT ARPC1 restored normal trichome structure and density, and terpene synthesis. Structural and amino acid sequence analysis showed that there was a missplicing mutation in the hl-3 mutant, which was responsible for the abnormal trichome structure and density, and impaired terpene synthesis. Overall, the findings of this study demonstrated that ARPC1 is involved in regulating trichome structure and terpene synthesis in tomato.

SlHair2 Regulates the Initiation and Elongation of Type I Trichomes on Tomato Leaves and Stems.

Trichomes are hair-like structures that are essential for abiotic and biotic stress responses. Tomato Hair (H), encoding a C2H2 zinc finger protein, was found to regulate the multicellular trichomes on stems. Here, we characterized Solyc10g078990 (hereafter Hair2, H2), its closest homolog, to examine whether it was involved in trichome development. The H2 gene was highly expressed in the leaves, and its protein contained a single C2H2 domain and was localized to the nucleus. The number and length of type I trichomes on the leaves and stems of knock-out h2 plants were reduced when compared to the wild-type, while overexpression increased their number and length. An auto-activation test with various truncated forms of H2 using yeast two-hybrid (Y2H) suggested that H2 acts as a transcriptional regulator or co-activator and that its N-terminal region is important for auto-activation. Y2H and pull-down analyses showed that H2 interacts with Woolly (Wo), which regulates the development of type I trichomes in tomato. Luciferase complementation imaging assays confirmed that they had direct interactions, implying that H2 and Wo function together to regulate the development of trichomes. These results suggest that H2 has a role in the initiation and elongation of type I trichomes in tomato.