Proteomic analysis of pathogenesis-related proteins (PRs) induced by compatible and incompatible interactions of pepper mild mottle virus (PMMoV) in Capsicum chinense L3 plants

Resistance conferred by the L-3 gene is active against most of the tobamoviruses, including the Spanish strain (PMMoV-S), a P-1,P-2 pathotype, but not against certain strains of pepper mild mottle virus (PMMoV), termed P-1,P-2,P-3 pathotype, such as the Italian strain (PMMoV-I). Both viruses are nearly identical at their nucleotide sequence level (98%) and were used to challenge Capsicum chinense PI159236 plants harbouring the L-3 gene in order to carry out a comparative proteomic analysis of PR proteins induced in this host in response to infection by either PMMoV-S or PMMoV-I. PMMoV-S induces a hypersensitive reaction (HR) in C. chinense PI159236 plant leaves with the formation of necrotic local lesions and restriction of the virus at the primary infection sites. In this paper, C. chinense PR protein isoforms belonging to the PR-1, beta-1,3-glucanases (PR-2), chitinases (PR-3), osmotin-like protein (PR-5), peroxidases (PR-9), germin-like protein (PR-16), and PRp27 (PR-17) have been identified. Three of these PR protein isoforms were specifically induced during PMMoV-S-activation of C. chinense L-3 gene-mediated resistance: an acidic beta-1,3-glucanase isoform (PR-2) (M-r 44.6; pI 5.1), an osmotin-like protein (PR-5) (M-r 26.8; pI 7.5), and a basic PR-1 protein isoform (M-r 18; pI 9.4-10.0). In addition, evidence is presented for a differential accumulation of C. chinense PR proteins and mRNAs in the compatible (PMMoV-I)-C. chinense and incompatible (PMMoV-S)-C. chinense interactions for proteins belonging to all PR proteins detected. Except for an acidic chitinase (PR-3) (M-r 30.2; pI 5.0), an earlier and higher accumulation of PR proteins and mRNAs was detected in plants associated with HR induction. Furthermore, the accumulation rates of PR proteins and mRNA did not correlate with maximal accumulation levels of viral RNA, thus indicating that PR protein expression may reflect the physiological status of the plant.