AIR12, a b-type cytochrome of the plasma membrane of Arabidopsis thaliana is a negative regulator of resistance against Botrytis cinerea

AIR12 (Auxin Induced in Root culture) is a single gene of Arabidopsis that codes for a mono-hemecytochrome b. Recombinant AIR12 from Arabidopsis accepted electrons from ascorbate or superoxide,and donated electrons to either monodehydroascorbate or oxygen. AIR12 was found associated in vivoto the plasma membrane. Though linked to the membrane by a glycophosphatidylinositol anchor, AIR12is a hydrophilic and glycosylated protein predicted to be fully exposed to the apoplast. The expressionpattern of AIR12 in Arabidopsis is developmentally regulated and correlated to sites of controlled cellseparation (e.g. micropilar endosperm during germination, epidermal cells surrounding the emerginglateral root) and cells around wounds. Arabidopsis (Landsberg erecta-0) mutants with altered levels ofAIR12 did not show any obvious phenotype. However, AIR12-overexpressing plants accumulated ROS(superoxide, hydrogen peroxide) and lipid peroxides in leaves, indicating that AIR12 may alter the redoxstate of the apoplast under particular conditions. On the other hand, AIR12-knock out plants displayed astrongly decreased susceptibility to Botrytis cinerea infection, which in turn induced AIR12 expression insusceptible wild type plants. Altogether, the results suggest that AIR12 plays a role in the regulation ofthe apoplastic redox state and in the response to necrotrophic pathogens. Possible relationships betweenthese functions are discussed.