TTG2 defines trichome cell shape by modulating microtubules and actin cytoskeleton in Arabidopsis

The Arabidopsis TRANSPARENT 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 of TTG2 was previously shown to reduce or eliminate trichome branching. Here, we report the identification of a new allele of TTG2 , ttg2-6 . In contrast to the ttg2 mutants described before, ttg2-6 displays unique trichome phenotypes. Some ttg2-6 mutant trichomes are hyperbranched, whereas others are hypobranched, distorted, or clustered. Further, we found that in addition to specifically activating R3 MYB transcription factor TRIPTYCHON ( TRY ) to promote trichome branching, TTG2 also integrates cytoskeletal signaling to regulate trichome morphogenesis. The ttg2-6 trichomes 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 of BRICK1 ( BRK1 ), a subunit of the actin nucleation promoting complex SCAR/WAVE. Collectively, taking advantage of ttg2-6 , we uncovered new functions for TTG2 in facilitating cMT and F-actin cytoskeleton-dependent trichome development. Our evidence for a direct relationship between TTG2 and cytoskeletal regulators establishes an unprecedented understanding of cellular signaling events downstream of the core transcriptional regulation during trichome development in Arabidopsis.