Format: ORAL

Rafael Jorge León Morcillo1 , Jesús Leal-López1 , Alberto Férez-Gómez1 , Lidia LópezSerrano1 , Edurne Baroja-Fernández2 , Samuel Gámez-Arcas3 , Germán Tortosa4 , Leonel E. López5 , José Manuel Estevez5,6 , Verónica G. Doblas1 , Laura Frías-España1 , María Dolores García-Pedrajas1 , Jorge Sarmiento-Villamil1 and Javier Pozueta-Romero1

1 Institute for Mediterranean and Subtropical Horticulture “La Mayora” (IHSM), CSIC-UMA, Campus de Teatinos, Avda. Louis Pasteur, 49, 29010 Málaga, Spain. 2 Instituto de Agrobiotecnología (IdAB), CSIC-Gobierno de Navarra. Iruñako etorbidea 123, 31192 Mutiloabeti, Nafarroa, Spain. 3 Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas (CSIC)- Universidad de Sevilla, Sevilla, Spain 4 Department of Soil and Plant Microbiology, Estación Experimental del Zaidín (EEZ-CSIC), Profesor Albareda, 1, 18008 Granada, Spain 5 Fundación Instituto Leloir and IIBBA-CONICET, Av. Patricias Argentinas 435, Buenos Aires CP C1405BWE, Argentina. 6 Centro de Biotecnología Vegetal (CBV), Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago, Chile and ANID - Millennium Science Initiative Program - Millennium Nucleus for the Development of Super Adaptable Plants (MN-SAP), Santiago, Chile.

In nature, plants and microorganisms communicate with each other by exchanging different signaling compounds including volatile compounds (VCs), some of which have biostimulating properties. In Arabidopsis, VCs from the fungal phytopathogen Penicillium aurantiogriseum promote growth, photosynthesis and root hair (RH) proliferation and hyper-elongation through mechanisms involving ethylene, auxin and photosynthesis signaling. A striking alteration in the proteome of roots of fungal VCtreated plants involves strong up-regulation of RALF22. To test the possible involvement of the RALF22 in the fungal VC-promoted RH changes, we characterized the RH responses of ralf22 and fer-4 plants impaired in RALF22 and its receptor FERONIA to VCs emitted by P. aurantiogriseum. We found that these plants were unresponsive in terms of VC-promoted RH elongation and proliferation. Unlike in WT roots, fungal VCs did not enhance the transcript levels of RALF22 in roots of fer-4 and ethylene- and auxin- insensitive mutants, and those of RH-related, ethylene-responsive genes (e.g. RSL2, RSL4, RHD2, PRX1 and PRX44) in ralf22 and fer-4 roots. Finally, we identified ethylene as the bioactive fungal VC, as VCs of ?efeA strains of P. aurantiogriseum cultures impaired in ethylene synthesis weakly promoted RH proliferation and elongation in exposed plants. Collectively, our results demonstrate that RALF22-FERONIA complex is a key determinant of the ethylene, auxin and photosynthesis signaling-mediated RH response to fungal ethylene emissions.