Characterization of a leucine-rich repeat receptor-like protein kinase (LRPK) gene from Japanese pear and its possible involvement in scab resistance

Abstract

A gene encoding a leucine-rich repeat receptor-like protein kinase (LRPK) was identified from Japanese pear (Pyrus pyrifolia var. culta) using reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) PCR. The Japanese pear LRPKp protein was composed of a leucine-rich extracellular ligand-binding domain, a transmembrane-spanning segment, and a cytoplasmic kinase domain; it had the highest sequence homology with apple LRPKm and Arabidopsis receptor-like protein kinase (RLK). Southern blot analysis revealed that the LRPKp belongs to a multigenic family, and a polymorphism in restriction fragment length was observed among Asian and European pear cultivars. The LRPKp transcripts were present at a high level in leaves and at a low level in flowers, while no expression was detected in fruits. The expression pattern of LRPKp was also studied by real-time RT-PCR in the scab susceptible cv. Kousui and resistant cvs. Kinchaku and Flemish Beauty after challenge inoculation with Venturia nashicola, the causal agent of Japanese pear scab. Transcripts of LRPKp were transiently enhanced in both the susceptible Kousui and to a great extent in the non-host-resistant Flemish Beauty. However, in resistant Kinchaku, expression of this gene was only weakly enhanced. Moreover, treatment with a resistance inducer, acibenzolar-S-methyl (ASM), which significantly reduces scab severity on potted trees of Kousui, was also able to induce and to potentiate the expression of this gene after inoculation. This suggests that the LRPKp gene is possibly involved in ASM-induced resistance.