Overexpression of polygalacturonase-inhibiting protein 2 (PGIP2) of Chinese cabbage (Brassica rapa ssp. pekinensis) increased resistance to the bacterial pathogen Pectobacterium carotovorum ssp. carotovorum

Abstract

Polygalacturonase-inhibiting proteins (PGIPs) are plant cell wall glycoproteins that can inhibit microbial polygalacturonase (PG) activity. In this study, we cloned five PGIP genes from Chinese cabbage (Brassica rapa ssp. pekinensis). Reverse transcription PCR expression analysis showed that the accumulation of BrPGIP transcripts differed among various tissues and in response to biotic (bacterial innoculation) and abiotic stresses (i.e., wounding, jasmonic acid, cold, NaCl, and dehydration treatment). Transcripts of BrPGIP1, BrPGIP3, and BrPGIP5 were detected in all tissues tested except the stamen, while BrPGIP2 transcripts were expressed in all tissues tested. Transcripts of BrPGIP4 were not expressed in cabbage. Innoculation with a bacterium that causes soft rot, Pectobacterium carotovorum ssp. carotovorum (Pcc), strongly induced transcripts of BrPGIP2; and expression occurred more rapidly in the resistant compared to the susceptible line. BrPGIP2 showed 50–99% similarity in amino acid sequences to extracellular PGIPs from other plants. In order to assess the role of BrPGIP2 protein in protecting plants from Pcc, we generated a number of transgenic tobacco and Chinese cabbage lines over-expressing BrPGIP2. PGIP from transgenic tobacco plants inhibited Pcc PG activity by 74%, while PGIP from wild-type tobacco plants gave only 43% Pcc PG inhibition. Transgenic Chinese cabbage plants also exhibited improved resistance to bacterial soft rot (up to 54%). PGIP from transgenic Chinese cabbage plants inhibited Pcc PG activity by 77%, while PGIP from wild-type plants showed only 8% Pcc PG inhibition. This is the first report showing the role of BrPGIPs in resistance to bacterial soft rot caused by Pcc.