Expression of two Sclerotinia sclerotiorum endo-PG genes correlates with endo-polygalacturonase activity during Glycine max colonization

Quantitative expression of Sclerotinia sclerotiorum genes encoding two endo-polygalacturonase (endo-PG) isoforms (PGa and PGb), malate dehydrogenase (MDH, a key enzyme in fungal biosynthetic pathway of oxalic acid), and plant polygalacturonase-inhibiting protein (PGIP) were monitored by real-time reverse transcription-polymerase chain reaction (qRT-PCR) during the early stages (0-48 h) of soybean seedling infection. The activity of the two endo-PGs was also investigated during plant infection. PGa and PGb activity reflected very closely the pattern of their transcript accumulation as determined by qRT-PCR. In particular, the PGb encoding gene (Sspgb) was induced at 8 h after inoculation and reached a maximum at 16 h; expression of the PGa encoding gene (Sspga) was comparatively lower, reaching its maximum level later and its rate of increase paralleled that of the S. sclerotiorum b-tubulin gene; the expression of the MDH encoding gene (Ssmdh) was maximal 16 h after infection; soybean pgip transcript began to accumulate 8 h after inoculation reaching a maximum after 24 h. Expression patterns of reported genes are discussed in relation to the ability of S. sclerotiorum to induce disease by regulating endo-PGs and oxalate accumulation to elude the effect of plant PGIP.