Pathogenesis‐related protein 10 isolated from hot pepper functions as a ribonuclease in an antiviral pathway

Summary A hot pepper (Capsicum annuum) cDNA clone encoding pathogenesis‐related protein 10 (CaPR‐10) was isolated by differential screening of a cDNA library prepared from pepper leaves inoculated with tobacco mosaic virus pathotype (TMV‐P0). CaPR‐10 transcripts were induced in the incompatible interaction with TMV‐P0 or Xanthomonas campestris pv. vesicatoria (Xcv) but not induced in the compatible interaction. Characterization of enzymatic properties of CaPR‐10 indicated that the recombinant protein exhibits a ribonucleolytic activity against TMV RNA, as well as against pepper total RNA, and shows its putative antiviral activity in several conditions. The CaPR‐10 protein existed at very low level in leaf tissue but was dramatically induced as soon as plants were inoculated with TMV‐P0, and this was correlated with the increase of its ribonucleolytic activity. Immunoblot analysis and pull‐down assays using proteins extracted from pepper leaves showed that TMV‐P0 inoculation led to the phosphorylation of CaPR‐10, a modification that should affect its capacity for RNase function. We present data that the induction and subsequent phosphorylation of CaPR‐10 increased its ribonucleolytic activity to cleave invading viral RNAs, and this activity should be important to its antiviral pathway during viral attack in vivo.