Genome-wide identification of the NAC family genes of adzuki bean and their roles in rust resistance through jasmonic acid signaling.

Background: Adzuki bean (Vigna angularis) rust, caused by the fungus Uromyces vignae, is an important disease affecting adzuki bean yield and quality. Previously, several NAC transcription factors (TFs) were induced by rust infection in a resistant adzuki bean variety, suggesting that NAC TF members may play important roles in rust resistance.

Results: To further explore the functions of NAC TFs in rust resistance and to provide a reference for resistant varietal breeding, 101 NAC TFs were identified from the adzuki bean genome. The synteny analysis revealed 25 pairs of VaNACs in the genome, which exhibited whole-genome/segmental duplication. Based on the phylogenetic relationships and conserved motif characteristics, the NAC TFs of V. angularis can be divided into 16 subfamilies. Previous transcriptome data showed that nine VaNACs are significantly induced by rust infection. Here, a cis-acting element analysis of these nine genes revealed that most contain hormone responsive elements, such as abscisic acid and methyl jasmonate (MeJA). The expression levels of these nine VaNACs were dynamically regulated in response to exogenous MeJA treatment, as revealed by quantitative real-time PCR analysis. Among them, seven VaNACs exhibited significantly upregulated expression, peaking at 12 h post treatment (hpt) and remaining significantly higher than that of the untreated control group for 48 hpt. These results suggest that these VaNACs are responsive to MeJA signaling and may play roles in the early and sustained transcriptional regulation of stress-related pathways. The exogenous MeJA decreased rust severity on adzuki bean leaves by 45.68%. Additionally, the expression levels of these nine genes in adzuki bean leaves in response to rust infection after pretreatment with MeJA were investigated. The expression of VaNAC002 rapidly peaked at 24 h post inoculation (hpi) and remained significantly higher than the control from 120 to 192 hpi. Subsequently, transient overexpression of VaNAC002 significantly enhanced the resistance of tobacco to Botrytis cinerea, indicating that VaNAC002 positively regulates plant disease resistance.

Conclusion: These findings suggest that adzuki bean NAC family members may play important roles in disease resistance through JA signaling, with VaNAC002 having a positive regulatory role in plant immunity.