Characterization of Fusarium-induced expression of flavonoids and PR genes in maize

In maize, Fusarium ear rots lead to contamination of grains with mycotoxins and loss of yield. We tested if induced expression of 3-deoxyanthocyanidins and related 3-deoxyflavonoid (flavan-4-ols) compounds in maize silks and kernels impart resistance to Fusarium ear rot. In maize, condensed flavan-4-ols (phlobaphenes) accumulate in floral organs including silks and kernel pericarps and their biosynthesis is regulated by Pericarp color1 (P1) and a linked paralog P2. Three maize lines differing for allelic constitution at the P locus were compared for their response to Fusarium verticillioides and F. graminearum. The moderately resistant maize line P1-rr4B2 carrying both the P1 and the P2 gene showed enhanced accumulation of 3-deoxyanthocyanidins in inoculated silks. The line 4Co63 carrying only the P2 gene exhibited highest resistance to F. verticillioides. Expression data revealed that flavonoid pathway genes were active during the early stages of silk development. In kernels, however, induction of the flavonoid pathway genes was later than that in silks, and higher transcriptional induction was observed in line carrying both P1 and P2 genes. Among the PR genes tested, PR-4 and PR-5 showed developmental as well as fungus-induced expression. Field based ear rot incidence could be correlated with the presence of functional P locus as well as genetic background of the tested maize lines.