Genome-Wide Identification and Expression of Chitinase Class I Genes in Garlic (Allium sativum L.) Cultivars Resistant and Susceptible to Fusarium proliferatum

Abstract

Vegetables of the Allium genus are prone to infection by Fusarium fungi. Chitinases of the GH19 family are pathogenesis-related proteins inhibiting fungal growth through the hydrolysis of cell wall chitin; however, the information on garlic (Allium sativum L.) chitinases is limited. In the present study, we identified seven class I chitinase genes, AsCHI1–7, in the A. sativum cv. Ershuizao genome, which may have a conserved function in the garlic defense against Fusarium attack. The AsCHI1–7 promoters contained jasmonic acid-, salicylic acid-, gibberellins-, abscisic acid-, auxin-, ethylene-, and stress-responsive elements associated with defense against pathogens. The expression of AsCHI2, AsCHI3, and AsCHI7 genes was constitutive in Fusarium-resistant and -susceptible garlic cultivars and was mostly induced at the early stage of F. proliferatum infection. In roots, AsCHI2 and AsCHI3 mRNA levels were increased in the susceptible and decreased in the resistant cultivar, whereas in cloves, AsCHI7 and AsCHI5 expression was decreased in the susceptible but increased in the resistant plants, suggesting that these genes are involved in the garlic response to Fusarium proliferatum attack. Our results provide insights into the role of chitinases in garlic and may be useful for breeding programs to increase the resistance of Allium crops to Fusarium infections.

Pathogenesis-Related Genes of PR1, PR2, PR4, and PR5 Families Are Involved in the Response to Fusarium Infection in Garlic (Allium sativum L.)

“…Our results indicate that the promoters of the AsPR genes contain 15 cis-regulatory elements involved in the response to hormones such as ABA, SA, MeJA, auxin, ET, and GA, as well as 12 elements associated with immune defense and response to elicitors and stresses such as anaerobic conditions, dehydration, low and high temperature, salinization, heavy metals, and wounding (Table 3). This regulatory profile is similar to those of class I chitinase genes of A. sativum (AsPR3) [28] and B. rapa [37]. Stress-responsive elements STRE, W-box, and WUN-motif, known to mediate pathogen-and/or elicitor-inducible transcription of chitinase genes [33,38,39], were found in the promoters of AsPR1, AsPR2, and AsPR5 (STRE), AsPR1f, g (W-box), and AsPR1, AsPR2, and AsPR4 (WUN-motif), confirming that the four identified PR families should be involved in the response to pathogens, including fungi.…”

“…cepae [29]. Furthermore, PR3 genes AsCHI2, AsCHI3, AsCHI5, and AsCHI7, encoding GH19 class I chitinases, have been shown to be involved in the response to F. proliferatum attack [28].…”

“…Strelets, resistant and susceptible to FBR, respectively, were kindly provided by the Federal Scientific Vegetable Center (Moscow region, Russia). The choice of cultivars was based on the similarity of morphological characteristics in order to exclude their influence on experimental results [28].…”

“…cepae) as well as by other Fusarium species, such as F. acutatum, F. anthophilium, and F. proliferatum [14,26]. Comparative studies of FBR-resistant and susceptible Allium genotypes have disclosed some of the possible biochemical and genetic mechanisms underlying plant susceptibility to FBR [27,28]. In our previous study, we have shown that garlic chitinases belonging to the PR3 family are involved in the immune response against Fusarium infection [28].…”

“…Comparative studies of FBR-resistant and susceptible Allium genotypes have disclosed some of the possible biochemical and genetic mechanisms underlying plant susceptibility to FBR [27,28]. In our previous study, we have shown that garlic chitinases belonging to the PR3 family are involved in the immune response against Fusarium infection [28]. However, there is little information regarding the immune defense function of other PR proteins in garlic [29,30].…”