Anti-fungal activity of maize silk proteins and role of chitinases in Aspergillus flavus resistance

Studies were conducted to identify proteins in maize silks that may be contributing to Aspergillus flavus resistance. We first performed bioassays using silk extracts collected from two A. flavus-resistant inbred lines and two susceptible inbred lines. Fungal biomass was quantified by measuring fluorescence of a green fluorescent protein (GFP)-tagged A. flavus and by measuring ergosterol levels. The silk extracts from resistant inbreds had greater anti-fungal activity compared to susceptible inbreds. Comparative proteomic analysis of the two resistant and susceptible inbreds led to the identification of several anti-fungal proteins. One of the anti-fungal proteins that we further investigated was chitinase. There were three chitinases that were differentially expressed in the resistant lines (PRm3 chitinase, chitinase I, and chitinase A). We conducted chitinase assays on silk proteins from extracts of resistant and susceptible inbred lines. Silk extracts from resistant inbred lines showed significantly higher activity in the resistant maize inbreds compared to the susceptible inbreds (P < 0.01). The differential expression of chitinases in maize resistant and susceptible inbred silks suggests that these proteins may contribute to A. flavus resistance.

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