MYB36 controls root cell elongation by modulating auxin response

Abstract

We and others [1,2] have studied the role of MYB36, an Arabidopsis R2R3-MYB class transcription factor as a master regulator of the differentiation of the endodermis during root development. We present here our results confirming that MYB36 promotes the development of the Casparian band in root endodermal cells by the transcriptional regulation of genes involved in localized lignin assembly and deposition. Moreover, the transcriptional and developmental outcome from MYB36 overexpression support the idea that MYB36 is also involved in the coordinated arrest of cell elongation in the differentiation zone by modulating auxin signalling/perception in the root. Arabidopsis transgenic lines overexpressing MYB36 have pleiotropic phenotypes in auxin-related growth and development, reduced sensitivity to exogenous auxin, and altered gene expression in response to auxin. Both the initiation and lateral root emergence were impaired when MYB36 was overexpressed, but the lateral root phenotype was partially rescued by auxin treatments. However the expression of DR5:GUS and LAX3:YFP marker genes were not properly induced by auxin in the roots confirming that MYB36 function affects auxin responses. The transcriptomic landscape of the MYB36 conditional overexpressing line reveals a strong down-regulation of auxin signallling in shoots 24 hours after induction. These results would explain the drastic effect on cell elongation/expansion when MYB36 is expressed ectopically in Arabidopsis supporting endodermal differentiation as a developmental shift for auxin regulation in the primary root. Kamiya, T, et al. (2015) Proc Natl Acad Sci USA 112(33):10533–10538. Liberman, LM, et al. (2015) Proc Natl Acad Sci USA 112(39):12099-104.