Abstract
The transcription factor Woolly (Wo) and its downstream gene CycB2 have been shown to regulate trichome development in tomato (Solanum lycopersicum). It has been demonstrated that only the gain-of-function allele of Slwo (SlWoV, the Slwo woolly motif mutant allele) can increase the trichome density; however, it remains unclear why the two alleles function differently in trichome development. In this study, we used Nicotiana benthamiana as a model and cloned the homologues of Slwo and SlCycB2 (named Nbwo and NbCycB2). We also constructed a Nbwo gain-of-function allele with the same mutation site as SlWoV (named NbWoV). We found that both Nbwo and NbWoV directly regulate NbCycB2 and their own expression by binding to the promoter of NbCycB2 and their own genomic sequences. As form of a feedback regulation, NbCycB2 negatively regulates trichome formation by repressing Nbwo activity at the protein level. We also found that mutations in the Nbwo woolly motif can prevent repression of NbWoV by NbCycB2, which results in a significant increase in the amount of active Nbwo proteins and in increases in trichome density and the number of branches. Our results reveal a novel reciprocal regulation mechanism between NbCycB2 and Nbwo during trichome formation in N. benthamiana.
Highlights
Trichomes are specialized epidermal protuberances that are found on aerial parts of most terrestrial plants
We found that mutations in the Nbwo woolly motif can prevent repression of NbWoV by NbCycB2, which results in a significant increase in the amount of active Nbwo proteins and in increases in trichome density and the number of branches
Phylogenetic analyses showed that Nbwo and NbCycB2 had the highest similarity with Slwo and SlCycB2, respectively (Supplementary Fig. S2a, b)
Summary
Trichomes are specialized epidermal protuberances that are found on aerial parts of most terrestrial plants They can be classified into different types according to cell numbers and shapes, namely unicellular/multicellular, and glandular/ non-glandular. (Oppenheimer et al, 1991; Walker et al, 1999; Payne et al, 2000).This transcriptional complex activates the expression of the homeodomain protein GLABROUS2 (GL2) to induce the formation of trichomes (Rerie et al, 1994; Grebe, 2012) It triggers the expression of single-repeat R3 MYBs including TRY (Schnittger et al, 1999), CPC (Wada et al, 1997), ETC1, ETC2, ETC3 (Kirik et al, 2004,Wester et al, 2009), and TCL2 (Gan et al, 2011), and these act as negative regulators of GL3 1816 | Wu et al. It has been shown that the networks that regulate unicellular trichomes do not function in the development of multicellular trichomes (Serna and Martin, 2006;Yang et al, 2011; Kang et al, 2016;Yan et al, 2017)
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