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<p>Citrus canker is a devastating disease caused by <i>Xanthomonas citri</i> subsp. <i>citri</i> (<i>Xcc</i>), which secretes the effector PthA4 into host plants to trigger transcription of the susceptibility gene <i>CsLOB1</i>, resulting in pustule formation. However, the molecular mechanism underlying CsLOB1-mediated susceptibility to <i>Xcc</i> remains elusive. This study identified <i>CsCEL20</i> as a target gene positively regulated by CsLOB1. Cell expansion and cell wall degradation were observed in sweet orange leaves after <i>Xcc</i> infection. A total of 69 cellulase genes were retrieved within the <i>Citrus sinensis</i> genome, comprising 40 endoglucanase genes and 29 glucosidase genes. Transcriptomic analysis revealed that expression levels of <i>CsCEL8</i>, <i>CsCEL9</i>, <i>CsCEL20,</i> and <i>CsCEL26</i> were induced by <i>Xcc</i> invasion in sweet orange leaves, but not in the resistant genotype Citron C-05. Among them, <i>CsCEL20</i> exhibited the highest expression level, with an over 430-fold increase following <i>Xcc</i> infection. Additionally, RT-qPCR analysis confirmed that <i>CsCEL20</i> expression was induced in susceptible genotypes (Sweet orange, Danna citron, Lemon) upon <i>Xcc</i> 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 <i>CEL20</i> promoters and exhibits a difference between eight susceptible citrus genotypes and three resistant ones. Moreover, <i>CsCEL20</i> expression was upregulated in <i>CsLOB1</i>-overexpression transgenic lines compared to the wild type. Dual-luciferase reporter assays indicated that CsLOB1 can target the -505&#xa0;bp to -168&#xa0;bp region of <i>CsCEL20</i> promoter to trans-activate its expression. These findings suggest that <i>CsCEL20</i> may function as a candidate gene for citrus canker development and may be a promising target for biotechnological breeding of <i>Xcc</i>-resistant citrus genotypes.</p>

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Identifying the role of cellulase gene CsCEL20 upon the infection of Xanthomonas citri subsp. citri in citrus

  • 期刊论文

  • 发表日期：

    2025年1月6日

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  • Yi Li,
  • Huijie Lou,
  • Hongyan Fu,
  • Hanying Su,
  • Chenxing Hao,
  • Jianming Luo,
  • Nan Cai,
  • Yan Jin,
  • Jian Han,
  • Ziniu Deng,
  • Yunlin Cao,
  • Xianfeng Ma

摘要

Citrus canker is a devastating disease caused by Xanthomonas citri subsp. citri (Xcc), which secretes the effector PthA4 into host plants to trigger transcription of the susceptibility gene CsLOB1, resulting in pustule formation. However, the molecular mechanism underlying CsLOB1-mediated susceptibility to Xcc remains elusive. This study identified CsCEL20 as a target gene positively regulated by CsLOB1. Cell expansion and cell wall degradation were observed in sweet orange leaves after Xcc infection. A total of 69 cellulase genes were retrieved within the Citrus sinensis genome, comprising 40 endoglucanase genes and 29 glucosidase genes. Transcriptomic analysis revealed that expression levels of CsCEL8, CsCEL9, CsCEL20, and CsCEL26 were induced by Xcc invasion in sweet orange leaves, but not in the resistant genotype Citron C-05. Among them, CsCEL20 exhibited the highest expression level, with an over 430-fold increase following Xcc infection. Additionally, RT-qPCR analysis confirmed that CsCEL20 expression was induced in susceptible genotypes (Sweet orange, Danna citron, Lemon) upon Xcc 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 CEL20 promoters and exhibits a difference between eight susceptible citrus genotypes and three resistant ones. Moreover, CsCEL20 expression was upregulated in CsLOB1-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 CsCEL20 promoter to trans-activate its expression. These findings suggest that CsCEL20 may function as a candidate gene for citrus canker development and may be a promising target for biotechnological breeding of Xcc-resistant citrus genotypes.