Mapping and functional analysis of four apple receptor-like protein kinases related to <Emphasis Type="Italic">LRPKm1</Emphasis> in <Emphasis Type="Italic">HcrVf2</Emphasis>-transgenic and wild-type apple plants

The Malus–Venturia inaequalis interaction is the most studied plant–pathogen interaction involving a woody species. Besides the cloning of an apple scab resistance gene HcrVf2, several sequences have been recently identified that are modulated after pathogen recognition in Vf-resistant genotypes. Among these, there is a putative leucine-rich repeat receptor-like protein kinase from the apple scab-resistant cv. Florina, named LRPKm1 that is induced after V. inaequalis inoculation and salicylic acid treatment. In this work, the isolation, characterization, and mapping of four new genes belonging to the LRPKm multigene family are reported. According to their cumulative expression profiles in HcrVf2-transgenic and wild-type apple plants treated with V. inaequalis, LRPKm genes have been divided in two groups. LRPKm1 and LRPKm3, giving a response related to the presence of HcrVf2, are probably involved in the recognition of pathogen-derived signals. LRPKm2 and LRPKm4, with an expression profile unrelated to the HcrVf2 gene, are putatively involved in the plant basal defense. Furthermore, we have localized LRPKm proteins at the cytological level in the plasma membrane of epidermal cells in resistant genotypes following pathogen challenge, thus confirming software predictions and molecular results. The possible involvement of LRPKm proteins in apple scab resistance and in the plant basal defense makes them attractive for a better comprehension of the molecular mechanisms of the signal transduction pathways after pathogen recognition.