AtMYB93 is a novel negative regulator of lateral root development in Arabidopsis

Abstract

Plant root system plasticity is critical for survival in changing environmental conditions. One important aspect of root architecture is lateral root development, a complex process regulated by hormone, environmental and protein signalling pathways.Here we show, using molecular genetic approaches, that the MYB transcription factor AtMYB93 is a novel negative regulator of lateral root development in Arabidopsis.We identify AtMYB93 as an interaction partner of the lateral-root-promoting ARABIDILLO proteins. Atmyb93 mutants have faster lateral root developmental progression and enhanced lateral root densities, while AtMYB93-overexpressing lines display the opposite phenotype. AtMYB93 is expressed strongly, specifically and transiently in the endodermal cells overlying early lateral root primordia and is additionally induced by auxin in the basal meristem of the primary root. Furthermore, Atmyb93 mutant lateral root development is insensitive to auxin, indicating that AtMYB93 is required for normal auxin responses during lateral root development.We propose that AtMYB93 is part of a novel auxin-induced negative feedback loop stimulated in a select few endodermal cells early during lateral root development, ensuring that lateral roots only develop when absolutely required. Putative AtMYB93 homologues are detected throughout flowering plants and represent promising targets for manipulating root systems in diverse crop species.

AtMYB93is an endodermis-specific transcriptional regulator of lateral root development in arabidopsis

“…Moreover, Atmyb93 mutant LRs are somewhat insensitive to exogenously applied auxin, while the primary root responds similarly to wild type plants, indicating that AtMYB93 activity is specific to root branching. 23 We speculate that AtMYB93 is part of an auxin-induced negative feedback module, which may allow the plant to make a LR in response to local auxin fluctuations only when they reach a certain threshold, ensuring that LRs only develop when absolutely required.…”

“…23 AtMYB93 expression is confined exclusively to roots and is induced specifically during LR initiation and the early stages of LRP formation. Atmyb93 mutants show increased LR initiation and faster developmental progression, while AtMYB93-overexpressing lines have fewer LRs that transit more slowly through development.…”

“…AtMYB93 promoter activity is exquisitely localized, being confined to just a few cells in the endodermis that overlie the initiating LRP 23 (Fig. 1B).…”

“…23 Interestingly, it was previously shown that AtMYB93 is a direct target of endodermis-specific transcription factor SCARE-CROW (SCR), which is itself implicated in ABA responses, with scr mutants being ABA-hypersensitive. 24 As mentioned previously, the endodermis regulates later LR development in response to salt stress.…”

Branching Out in Roots: Uncovering Form, Function, and Regulation

“…3) that, until recently, was one of the only regulators identified to have a role in prebranch site formation . AtMYB93, a member of the R2R3 MYB class of transcription factor, is expressed exclusively and transiently in root endodermal cells overlying new primordia, from where it negatively regulates lateral root development (Gibbs et al, 2014). AtMYB93 expression is auxin inducible, and Atmyb93 mutants exhibit reduced sensitivity to this key signal during lateral root development.…”