Abstract
Trichomes are unicellular or multicellular epidermal structures that play a defensive role against environmental stresses. Although unicellular trichomes have been extensively studied as a mechanistic model, the genes involved in multicellular trichome formation are not well understood. In this study, we first classified the trichome morphology structures in Capsicum species using 280 diverse peppers. We cloned a key gene (Hairiness) on chromosome 10, which mainly controlled the formation of multicellular non-glandular trichomes (types II, III, and V). Hairiness encodes a Cys2-His2 zinc-finger protein, and virus-induced gene silencing of the gene resulted in a hairless phenotype. Differential expression of Hairiness between the hairiness and hairless lines was due to variations in promoter sequences. Transgenic experiments verified the hypothesis that the promoter of Hairiness in the hairless line had extremely low activity causing a hairless phenotype. Hair controlled the formation of type I glandular trichomes in tomatoes, which was due to nucleotide differences. Taken together, our findings suggest that the regulation of multicellular trichome formation might have similar pathways, but the gene could perform slightly different functions in crops.
Highlights
Trichomes are specialized cell structures that commonly occur in the epidermis of terrestrial plants
Based on the statistics of the number of trichomes in different tissues of 280 lines, referring to Luckwill’s classification of trichome density of Lycopersicon (Luckwill, 1943), pepper trichomes were divided into four grades: abundant (800–1,500 number/cm2), medium (200–800 number/cm2), sparse (1–200 number/cm2), and no (0 trichomes)
The number of type III trichomes on young leaves and leaves of hairiness line were 2.5- to 13-fold and 2fold higher, respectively; the number of type II and III trichomes on hair line stems was 2- to 13-fold higher; and the number of type III trichomes on hair line calyxes was 7-fold higher than that on F1 progeny, whereas the hairless lines had no trichomes. These results suggest that the Hairiness gene in this study mainly controlled the formation of multicellular non-glandular trichomes in pepper
Summary
Trichomes are specialized cell structures that commonly occur in the epidermis of terrestrial plants. Trichomes can exhibit remarkable morphological variation between plant species. Trichomes can be morphologically classified based on the number of cells, or whether they are glandular or branched (Tetsuya et al, 2008; Pattanaik et al, 2014). Due to their special structure, trichomes can serve as a model to study plant cell differentiation (Johnson, 1975; Karabourniotis et al, 2010). Trichomes protect plants against biotic and abiotic stresses, arthropod herbivores, pathogens, and UV-B radiation and prevent water loss (Werker, 2000; Kennedy, 2003; Kang et al, 2014). Secondary metabolites in glandular trichomes have been utilized as food additives, in pharmaceuticals, and as natural pesticides (Aharoni et al, 2006; Schilmiller et al, 2008; Yang et al, 2015)
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