Accumulation of transcripts for pathogenesis–related proteins and peroxidase in rice plants triggered byPyricularia oryzae , Bipolaris sorokiniana and u.v. light

Abstract

A study of selected transcripts in rice leaves was performed using a number of cDNA clones from barley as probes. The transcripts for the pathogenesis–related proteins, PR-1, PR-2, PR-3, PR-4 and PR-5, and for a peroxidase were found to accumulate strongly in response to the non-rice pathogen Bipolaris sorokiniana and moderately in response to a virulent isolate of Pyricularia oryzae (Magnaporthe grisea) and u.v. light. A weak accumulation was observed in response to an avirulent isolate of P. oryzae. PR-protein transcript accumulation was seen 12 h after inoculation with B. sorokiniana and after exposure to u.v. light. These transcripts reached maximum accumulation levels at 24 h and all declined thereafter with the exception of the PR-4 transcript in response to B. sorokiniana. Maximum accumulation of the peroxidase transcript occurred at 12 h in response to both B. sorokiniana and u.v. light. These PR-protein and peroxidase transcripts were later expressed markedly in response to avirulent and virulent isolates of P. oryzae. They were barely detectable at the early time points, while maximum transcript levels occurred towards the end of the experiment, i.e. 120 h after inoculation. Interestingly, all these transcripts accumulated to a higher level in the compatible than in the incompatible interactions between rice and P. oryzae. Transcripts for chalcone synthase, oxalate oxidase and an oxalate oxidase-like protein were not detectable using the heterologous barley clones, whilst 14-3-3 protein and O -methyltransferase transcripts were seen to be constitutively expressed.