A Gene of Many Functions: Novel Roles for a Plant Epidermal Transcription Factor in Early Diverging Eudicots

Abstract

The epidermal transcription factors MIXTA/MIXTA-like modulate the differentiation of distinct cell identities in the epidermis of land plants. This study explored the evolutionary history and function of the MIXTA-like gene family in the early-diverging eudicot model Thalictrum. Phylogenetic analysis of the gene family revealed a lineage-specific duplication event that coincides with a Whole Genome Duplication (WGD) in the genus. In addition, T. thalictroides MIXTA-like gene was functionally characterized via targeted gene silencing, and a transcriptome analysis conducted to identify candidate targets. We found that TthMYBML2 modulates leaf trichome morphogenesis through a microtubule-associated mechanism. Overexpression assays in a heterologous system (tobacco) provided further evidence for the leaf trichome function, while uncovering a novel role in the promotion of stigmatic papillae elongation. The latter finding, combined with the high differential expression of specific MIXTA-like paralogs in carpels of polyploid wind-pollinated Thalictrum suggests that MIXTA-like duplications may be implicated in the development of the long stigmatic papillae in the feathery stigmas of those species.