O-glycosylated AGP21 acts on Brassinosteroid pathway to modulate root hair cell fate in Arabidopsis.

ESTEVEZ, JOSE M.; BORASSI, CECILIA; CARIGNANI SARDOY, MARIANA

San Jose

Congreso; Plant Biology 2019; 2019

American Society of Plant Biologists

Root hairs (RH) are single cells that develop from a group of specialized epidermal cells referred to as trichoblasts while cells that lack them are called atrichoblasts. RH cell fate is regulated by a complex of transcription factors that promotes the expression of the homeodomain protein GLABRA 2 (GL2), which ultimately blocks the RH pathway by inhibiting ROOT HAIR DEFECTIVE 6 (RHD6). The suppression of GL2 expression triggers epidermal cells to enter into the RH cell fate program by the concomitant activation of RHD6 and a downstream series of TFs including ROOT HAIR DEFECTIVE 6 LIKE-4 (RSL4) and downstream target genes. Cell fate in the root epidermis is influenced by phytohormones like auxins and Brassinosteroids (BR). It has been shown that in the absence of BR, phosphorylated BIN2 (a Type-II GSK3-like kinase) promotes the inhibition of a protein complex leading to the down-regulation of the main RH repressor GL2. In this work, an arabinogalactan protein (AGP) mutant agp21 as well as β-Glucosyl Yariv (β-Glc-Y) treatment (that disturbs AGPs) and several mutants deficient in AGP modifications, all trigger an abnormal RH cell fate phenotype reminiscent of mutants with deficient BR responses. We have found that an O-glycosylated AGP21-peptide positively regulated by BZR1, impacts on RH cell fate by disturbing GL2 expression in a BIN2 dependent manner. Together, these results show that disruption of cell surface AGPs, and in particular AGP21, interfere in a specific manner with BR perception and BIN2 mediated responses on the RH repressor GL2 in root epidermal cells in Arabidopsis thaliana.