Protease inhibitor expression in soybean roots exhibiting susceptible and resistant interactions with soybean cyst nematode.

Protease inhibitors play a role in regulating proteases during cellular development and in plant defense. We cloned and sequenced cDNA encoding six protease inhibitors expressed in soybean roots infected with soybean cyst nematode (SCN) and determined their expression patterns. Four of these protease inhibitors are novel and have not been reported previously. Using RT-PCR, we measured the relative transcript levels of each protease inhibitor in roots of the soybean cv. Peking inoculated with either SCN TN8 to examine the expression of protease inhibitors during the susceptible interaction or with SCN NL1-RHg representing the resistant interaction. Within 12 to 24 hours, mRNA transcripts encoding five of the six protease inhibitors were more highly elevated in soybean roots exhibiting the susceptible interaction than the resistant interaction. Transcripts encoding two protease inhibitors possessing Kunitz trypsin inhibitor domains were induced 37- and 27-fold in the susceptible interaction within 1 dpi, but were induced only 5- to 7-fold in roots displaying the resistant interaction. Our results indicate that soybean roots recognize differences between these two SCN populations before the nematodes initiate a feeding site, and accordingly the roots express transcripts encoding soybean protease inhibitors differentially. These transcripts were generally less abundant in roots exhibiting the resistant interaction.