PR10 expression in maize and its effect on host resistance against Aspergillus flavus infection and aflatoxin production.

Maize (Zea mays L.) is a major crop susceptible to Aspergillus flavus infection and subsequent contamination with aflatoxins, the potent carcinogenic secondary metabolites of the fungus. Protein profiles of maize genotypes resistant and susceptible to A. flavus infection and/or aflatoxin contamination have been compared, and several resistance-associated proteins have been found, including a pathogenesis-related protein 10 (PR10). In this study, RNA interference (RNAi) gene silencing technology was employed to further investigate the importance of PR10. An RNAi gene silencing vector was constructed and introduced into immature Hi II maize embryos through both bombardment and Agrobacterium infection procedures. PR10 expression was reduced by 65% to more than 99% in transgenic callus lines from bombardment. The RNAi-silenced callus lines also showed increased sensitivity to heat stress treatment. A similar reduction in PR10 transcript levels was observed in seedling leaf and root tissues developed from transgenic kernels. When inoculated with A. flavus, RNAi-silenced mature kernels produced from Agrobacterium-mediated transformation showed a significant increase in fungal colonization and aflatoxin production in 10 and six, respectively, of 11 RNAi lines compared with the non-silenced control. Further proteomic analysis of RNAi-silenced kernels revealed a significant reduction in PR10 production in eight of 11 RNAi lines that showed positive for transformation. A significant negative correlation between PR10 expression at either transcript or protein level and kernel aflatoxin production was observed. The results indicate a major role for PR10 expression in maize aflatoxin resistance.