Characterization of VQ Gene Family and Its Roles in Anthracnose Stress Responses of Juglans regia

VQ proteins, characterized by the FxxhVQxhTG motif, comprise a family involved in plant defense responses. Walnut (Juglans regia) yield and quality are severely affected by Colletotrichum gloeosporioides causing anthracnose, necessitating understanding the molecular response mechanisms. Therefore, in this study, the VQ genes of J. regia (named JrVQ) were identified from the walnut genome based on bioinformatics tools (such as PFAM and SMART), and their transcriptional changes in response to anthracnose under controlled inoculation and natural infection in two varieties (resistant ‘Xiangling’ and susceptible ‘Xilin3’) were analyzed using real-time quantitative PCR. As a result, 15 JrVQ genes (JrVQ1 to JrVQ15) were identified, whose open reading frames were 225 to 1,182 bp with isoelectric points ranging from 5.94 to 10.67. These JrVQs were distributed across nine chromosomes out of a total of 32. Their protein secondary structures consisted of α-helices, extended chains, and random coils. Most of the cis-elements in the promoters of JrVQ genes were related to stress response. The expression of JrVQ genes could be induced in leaves, green husks, and stems and reached maximum level at 6 or 9 dpi under both conditions. Especially the expression of JrVQ10 and JrVQ9, the most prominent ones, reached 6.11 and 5.96, respectively. Moreover, the induction of JrVQs was higher in ‘Xiangling’ than in ‘Xilin3’ and was significantly correlated with the C. gloeosporioides infection process as well as the activity of total antioxidant enzyme, a key indicator of anthracnose resistance. These results suggested the involvement of JrVQs in the regulation of walnut anthracnose response.