The role of RBOH-type NADPH oxidases in compatibility of barley with fungal organisms
Final Report Abstract
Plant NADPH oxidases (RBOHs) are organized in gene families comprising several members. They are prominent sources of reactive oxygen species in signal transduction, development and in interaction with pathogens. RBOHs appear as key factors in the pathogen response and control of cell-death. However, little genetic evidence exists for the function of diverse RBOHs in agronomically relevant monocots. Therefore, we analysed the function of individual barley RBOH family members in signalling and basal resistance to powdery mildew fungi. Besides HvRboh F2 we identified one more RBOH member based on the prerequisite to be expressed in leaves and according to Y2H data showing interaction of HvRBOH B2 with RAC1, a potential positive regulator of the oxidative burst. Transient knock-down or overexpression of HvRboh B2 resulted in higher or lower susceptibility to Bgh in single epidermis cells, respectively. Stable transgenic barley lines characterized by a knockdown of HvRboh B2, however, did not yield significant differences in susceptibility to Bgh. The absence of a clear phenotype in stable transformed plants compared to transient knock-down might be explained by a compensation of loss of HvRBOH B2 by other HvRBOH isoforms. To complete the analysis of HvRBOH B2 function, stable transgenic overexpressor lines were generated for further investigations. By contrast to HvRBOH B2, stable transgenic HvRboh F2 knock-down lines are more susceptible to Bgh but are also characterized by pleiotropic effects, such as a dwarf phenotype in adult plants. Fully grown leaves of HvRboh F2 knock-down lines show ectopic cell-death and as a consequence they are incompatible with the biotrophic fungus Bgh. Interestingly, fully grown leaves of HvRboh F2 knock-down lines are impaired in the expression of key fermentative enzymes ADH and LDH. Our group established a function of ADH in the barley-Bgh pathosystem. HvAdh1 knock-down or overexpression results in an reduced or increased susceptibility to Bgh in transient as well as stable transgenic lines, respectively. These data give for the first time genetic evidence for a role of HvRBOH F2 in regulation of key metabolic enzymes and suggest ADH and LDH as molecular targets downstream of RBOH. HvRBOH F2 mediated regulation of ADH provides a link between RBOH-mediated pathogen phenotypes and ADH function. This set of data is the basis for a future second publication on HvRBOH F2 function, which will focus on regulation of key fermentative enzymes and their implication in the pathogen response and cell-death regulation.
Publications
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RBOHF2 of barley is required for normal development of basal penetration resistance to the parasitic fungus Blumeria graminis f.sp. hordei. Molecular Plant-Microbe Interaction 23. 2010: 1143-1150.
Proels RK, Oberhollenzer K, Pathuri IP, Hensel G, Kumlehn J, Hückelhoven R.
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The subcellular localization of Tubby-like proteins and participation in stress signaling and root colonization by the mutualist Piriformospora indica. Plant Physiol. 160. 2012: 349-364.
Reitz MU, Bissue JK, Zocher K, Attard A, Hückelhoven R, Becker K, Imani J, Eichmann R, Schäfer P
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Reduced carbohydrate availability enhances susceptibility of Arabidopsis towards Colletotrichum higginsianum. Plant Physiol. 162. 2013: 225–238
Engelsdorf T, Horst RJ, Pröls R, Pröschel M, Dietz F, Hückelhoven R, Voll LM
