Role of pathogenesis-related genes in rice-gall midge interactions

Abstract

A sequence encoding putative pathogenesis-related protein OsPR10α (GenBank accession no. GQ487633) was identified from suppression subtractive hybridization cDNA library of rice cultivar Suraksha, after infestation with the Asian rice gall midge (Orseolia oryzae) involving incompatible interaction with hypersensitive reaction (HR). Full-length cloning (RACE) and homology search proved its identity as root-specific OsPR10α (RsOsPR10α). The expression of RsOsPR10α was analysed at different time intervals to understand its role in the resistance mechanism in rice against the pest. Real-time PCR detected significant upregulation of the gene, 40.4 and 23.5-fold at 24 and 120 h after infestation respectively, with the avirulent gall midge biotype 1 (GMB1) in Suraksha. Such upregulation was not observed after infestation with the virulent biotype (GMB4M). Significantly, RsOsPR10α expression was not upregulated in the cultivar Kavya, exhibiting resistance without HR against GMB1 or in the susceptible cultivar TN1 with either of the biotypes. Similar expression analysis of two other PR genes, OsPR1a and OsPR2, did not reveal significant changes in the transcript levels. Further, sequence analysis of full-length RsOsPR10α and its promoter region from the three cultivars revealed mutations in Kavya at four putative cis-acting elements, viz. PAL A box binding site, GT-1 binding site, bZIP binding site and GATA binding site. These results suggest that RsOsPR10α plays an important role in the events leading to gall midge resistance with HR. They also demonstrate that rice–gall midge interactions share similarities with the reported rice–pathogen interactions rather than with in rice–insect interactions. To the best of our knowledge, there are no reports implicating PR10a gene in plant resistance against insects.