Ubiquitin ligase PUB41 modulates root hair development in Arabidopsis via interaction with the auxin polar transporter PIN2

Abstract

Root hairs are short-lived, elongated tubular extensions of epidermal cells, that increase the surface area improving absorption of water and nutrients. Root hair development is affected by developmental, environmental, and hormonal cues, primarily Auxin. Auxin is synthesized in shoot and root apical transporters. Here, we report that mutants of the Arabidopsis PLANT U-BOX41 (AtPUB41) gene encoding a ubiquitin ligase (E3) develop fewer and shorter root hairs than wild-type (WT) plants. pub41 mutants are not impaired in sensing and responding to exogenous auxin, suggesting that the root hair phenotype may result from a change in auxin levels and/or distribution. Indeed, Auxin enhances the steady-state levels of PUB41 transcript and protein in the roots. A catalytically inactive decoy protein lacking the U-box, PUB41({Delta}U), complements the sparse root hair phenotype of pub41 mutants to the same extent as full-length PUB41. Plants expressing PUB41({Delta}U) are hyperresponsive to auxin-induced root hair development and PUB41({Delta}U) accumulates in the root elongation and differentiation zones, preferentially in trichoblast cells and their root hairs. Furthermore, in these cells, PUB41-eGFP and PUB41({Delta}U)-eGFP are primarily located on the anticlinal faces, as is the auxin PIN2 exporter. We show colocalization of PUB41({Delta}U)-eGFP and PIN2-mCherry, and binding in vitro of PUB41 to the cytoplasmic hydrophilic loop of PIN2. Moreover, PUB41({Delta}U) protein stabilizes PIN2 and enhances its abundance in the roots. Our results indicate that PUB41 modulates root hair development via interaction with PIN2. Significance StatementRoot hairs are extensions of the root epidermal cells, which are crucial for the uptake of water and nutrients from the soil. Root hair development is highly regulated and affected by developmental, environmental, and hormonal cues. In this study, we demonstrate that the auxin-induced ubiquitin ligase, PLANT U-BOX 41 (PUB41), regulates root-hair development by interacting with the auxin polar transporter PIN2 responsible for determining auxin levels.