Expressão diferencial de genes de resistência à antracnose do colmo (Colletotrichum graminicola) em germoplasma de milho tropical

Abstract

Anthracnose caused by the fungus Colletotrichum graminicola (Ces.) Wils. is one of the main stalk-base rots in maize. The use of resistant cultivars is the most efficient, economical and sustainable control strategy. In this study, a temporal analysis of gene expression of two inbred tropical maize lines inoculated with C. graminicola was performed. Two lines contrasting for resistance, L04-2 (resistant) and L99-4 (susceptible), were used and cultivated in two environmental conditions, growth chamber and greenhouse, and inoculated in the stalk with the pathogen at the V6 and VT stages, respectively. For mRNA extraction, pith tissue from the second internode of the stalks was collected at 0, 6, 12, 24, 48, 96, 168 and 336 hours after inoculation. Gene expression analysis was performed by RT-qPCR for eleven resistance/defense related genes, and the relative quantification of the expression of each gene was determined by the comparative Cq method. At the V6 stage, there was early differential expression for genes ZmPR5, ZmLOX3, ZmBB, ZmWIP1 and ZmCYP94B12, while at the VT stage, for genes ZmPR3, ZmPR5, ZmPR10.1, ZmLOX3, ZmLOX5, ZmBB, ZmWIP1 and ZmACO31, with a higher level of induction in resistant line L04-2 at both stages. The peak expression of ZmBB and ZmWIP1 genes at the V6 stage, and of ZmPR1, ZmPR3, ZmPR5, ZmPR10.1, ZmLOX5, ZmBB, ZmWIP1 and ZmACO31 genes at the VT stage, was reached earlier in the resistant line L04-2 compared to the susceptible line L99-4. The results showed that the expression of ZmPR5, ZmPR10.1, ZmLOX5, ZmBB, ZmWIP1 and ZmCYP94B12 genes was affected by developmental stage, with higher expression level at VT stage. At this stage, ZmWIP1 evidenced a remarkably contrasting expression pattern between lines, confirming the induction of resistance early in resistant line L04-2, and late in susceptible line L99-4. It is suggested that at the V6 stage, the ZmBB gene had the greatest contribution to resistance to C. graminicola, whereas at VT, the ZmLOX5 gene. The resistance to anthracnose stalk rot of line L04-2, is explained by a rapid induction of different plant defense genes, confirming its high resistance to C. graminicola. The gene expression results extended the scientific knowledge about the most effective genes for anthracnose stalk rot resistance in tropical maize germplasm, as well as the gene expression response of inbred lines dependent on the developmental stage (V6 or VT). The scientific knowledge obtained may assist in the development of maize cultivars with greater resistance to anthracnose stalk rot.