MYB36 regulates root cell elongation by modulating auxin response in Arabidopsis thaliana

Abstract

We and others [1,2] have studied the role of MYB36, an Arabidopsis R2R3-MYB class transcription factor (TF), as a master regulator of the differentiation of the endodermis during root development. Our results support that MYB36 regulates a developmental switch from proliferative to differentiated state that promotes the development of the Casparian band, in part by regulation of the expression of genes involved in the very localized lignin assembly and deposition in cells from root endodermis. The genetic and molecular mechanisms controlling the cell size in the root elongation zone and the regulators driving the coordinated arrest of cell elongation in the transition from elongation to differentiation zone, are still poorly understood. Here, we present the transcriptional and developmental outcome from MYB36 overexpression, which supports the idea that MYB36 is involved in this process 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 LAX3pro:YFP auxin-marker genes were not properly induced by auxin in the overexpressing line confirming that MYB36 function affects auxin responses. Moreover the transcriptome analysis of a line MYB36 conditionally overexpressing MYB36 revealed a strong down-regulation of auxin signalling in shoots 24 hours after induction. These results would explain the drastic effect on cell elongation/expansion when MYB36 is expressed ectopically in Arabidopsis 1 Kamiya, T, el al. (2015). Proc Natl Acad Sci USA 112(33):10533-10538. 2 Liberman, LM, el al. (2015). Proc Nall Acad Sci USA 112(39):12099-104.Peer Reviewe