Expression of Genes Involved in Anthracnose Resistance in Chili (Capsicum baccatum) 'PBC80'-Derived Recombinant Inbred Lines

Abstract

Chili anthracnose has long been a threat to chili production worldwide. Capsicum baccatum 'PBC80' has been identified as a source of resistance to anthracnose. Recently, a QTL for ripe fruit resistance from 'PBC80'-derived RILs was located on chromosome 4 (123 Mb) and contained over 80 defense-related genes. To identify the genes most related to anthracnose resistance, a fine map of the QTL region was developed using single-marker analysis. Nine genes were selected from the new QTL (1.12 Mb) to study their expression after being challenged with Colletotrichum scovillei 'MJ5' in two different RIL genotypes (Resistance/Resistance or R/R and Susceptible/Susceptible or S/S) at 0, 6 and 12 h. Of the nine genes, LYM2, CQW23_09597, CLF, NFXL1, and PR-14 were significantly up-regulated, compared to the control, in the R/R genotype. ERF was up-regulated in both chili genotypes. However, the expression was relatively and constantly low in the S/S genotype. Most up-regulated genes reached the highest peak (2.3-4.5 fold) at 6 h, except for ERF, which had the highest peak at 12 h (6.4 fold). The earliest and highest expressed gene was a pathogen receptor, LYM2.

Keywords: Colletotrichum scovillei; defense-related genes; hypersensitive reaction; microinjection; qRT-PCR; wounded inoculation.

Figure 1

A graphical summary of the study methodology.

Figure 2

Fine map of the QTL RA80f6_r1 after the addition of the silico and SNP markers (left); LOD values of all the markers in the QTL derived from single marker analysis (right), indicating SNP309 and Silico09 had the highest LODs (5.2 and 5.9, respectively).

Figure 3

Two selected RILs G1-017130 with R/R (top) and G1-017264 with S/S (bottom) phenotypes for the gene expression study.

Figure 4

Anthracnose severity scores on mature green and ripe fruit in Capsicum baccatum ‘PBC80’ and ‘CA1316’, and in the 29 RILs. The disease scores 0–7 are found in the RILs; score 0 = G1-017425, score 1 = G1-017325 (green) and G1-017473 (ripe), score 3 = G1-017579 (green) and G1-017540 (ripe), score 5 = G1-017541 (green) and G1-017233 (ripe) and score 7 = G1-017267.

Figure 5

Relative expression levels 0–12 h post fruit inoculation with MJ5 and water of the nine genes in two chili genotypes: R/R + water (grey), R/R + MJ5 (black), S/S + water (white), and S/S + MJ5 (dot). The vertical bars represent standard deviation of the means based on 2-way ANOVA; *, **, *** and **** indicate statistically significant differences compared to the same chili genotype inoculated with water at 0 h (control) at p < 0.05, p < 0.01, p < 0.001 and p < 0.0001, respectively, by Tukey’s HSD test.