Cell surface O-glycosylated AGP21 peptide acts on the Brassinosteroids pathway to modulate root hair cell fate

GLOAZZO DOROSZ, JAVIER; BORASSI, CECILIA; CARIGNANI SARDOY, MARIANA; RICARDI, MARTINIANO

Simposio; III Simposio Argentino de Glicobiología; 2019

Cell surface O-glycosylated AGP21 peptide acts on the Brassinosteroids pathway to modulate root hair cell fate Cecilia Borassi1,#, Javier Gloazzo Dorosz1,#, Martiniano M. Ricardi2,#,*, Mariana Carignani1, Laercio Pol Fachin3, Hugo Verli4 & José M. Estevez1,?1Fundación Instituto Leloir, Av. Patricias Argentinas 435, Buenos Aires CP C1405BWE, Argentina. 2Instituto de Fisiología, Biología Molecular y Neurociencias (IFIByNE-CONICET), Departamento de Fisiología y Biología Molecular y Celular (FBMC), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires C1428EGA, Argentina. 3Aggeu Magalhães Research Center, Oswaldo Cruz Foundation, Recife, Brazil.4Centro de Biotecnologia, Universidade Federal do Rio Grande do Sul CP 15005, Porto Alegre 91500-970 RS, Brazil. #co-first authors. Email: cborassi@leloir.org.arRoot hairs (RH) develop from a group of specialized epidermal cells referred to as trichoblasts while cells that lack them are called atrichoblasts. Root hair 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 downstream including ROOT HAIR DEFECTIVE 6 LIKE-4 (RSL4) [1] and downstream target genes. Cell fate in the root epidermis is influenced by hormones like Brassinosteroid (BR). In the absence of BR, phosphorylated BIN2 (a Type-II GSK3-like kinase) promotes the inhibition of a protein complex that directly impacts on the down-regulation of the main RH repressor GL2 [2]. 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 root hair (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-BIN2 downstream effect on the RH repressor GL2 in root epidermis cells.