Identifying the role of cellulase gene upon the infection of subsp. in citrus.

UNLABELLED

Citrus canker is a devastating disease caused by subsp. (), which secretes the effector PthA4 into host plants to trigger transcription of the susceptibility gene , resulting in pustule formation. However, the molecular mechanism underlying CsLOB1-mediated susceptibility to remains elusive. This study identified as a target gene positively regulated by CsLOB1. Cell expansion and cell wall degradation were observed in sweet orange leaves after infection. A total of 69 cellulase genes were retrieved within the genome, comprising 40 endoglucanase genes and 29 glucosidase genes. Transcriptomic analysis revealed that expression levels of , , and were induced by invasion in sweet orange leaves, but not in the resistant genotype Citron C-05. Among them, exhibited the highest expression level, with an over 430-fold increase following infection. Additionally, RT-qPCR analysis confirmed that expression was induced in susceptible genotypes (Sweet orange, Danna citron, Lemon) upon invasion, but not in resistant genotypes (Citron C-05, Aiguo citron, American citron). A Single-Nucleotide Polymorphism (SNP) at -423 bp was identified in the promoters and exhibits a difference between eight susceptible citrus genotypes and three resistant ones. Moreover, expression was upregulated in -overexpression transgenic lines compared to the wild type. Dual-luciferase reporter assays indicated that CsLOB1 can target the -505 bp to -168 bp region of promoter to trans-activate its expression. These findings suggest that may function as a candidate gene for citrus canker development and may be a promising target for biotechnological breeding of -resistant citrus genotypes.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11032-024-01531-3.