TTG2defines trichome cell shape by modulating microtubules and actin cytoskeleton in Arabidopsis

Abstract

AbstractThe ArabidopsisTRANSPARENT TESTA GLABRA2(TTG2) gene encodes a WRKY transcription factor that regulates a range of development events like trichome, seed coat, and atrichoblasts formation. Loss-of-function ofTTG2was previously shown to reduce or eliminate trichome branching. Here, we report the identification of a new allele ofTTG2,ttg2-6. In contrast to thettg2mutants described before,ttg2-6displays unique trichome phenotypes. Somettg2-6mutant trichomes are hyperbranched, whereas others are hypobranched, distorted, or clustered. Further, we found that in addition to specifically activating R3 MYB transcription factorTRIPTYCHON(TRY) to promote trichome branching,TTG2also integrates cytoskeletal signaling to regulate trichome morphogenesis. Thettg2-6trichomes display aberrant cortical microtubules (cMTs) and cortical actin filaments (F-actin) configurations. Moreover, genetic and biochemical analysis showed that TTG2 could directly bind and regulate the expression ofBRICK1(BRK1), a subunit of the actin nucleation promoting complex SCAR/WAVE. Collectively, taking advantage ofttg2-6, we uncovered new functions forTTG2in facilitating cMT and F-actin cytoskeleton-dependent trichome development. Our evidence for a direct relationship betweenTTG2and cytoskeletal regulators establishes an unprecedented understanding of cellular signaling events downstream of the core transcriptional regulation during trichome development in Arabidopsis.