CsLOB1 regulates susceptibility to citrus canker through promoting cell proliferation in citrus

Area of Science:

• Plant Molecular Biology
• Plant Pathology
• Genetics

Background:

• Citrus bacterial canker, caused by Xanthomonas citri subsp. citri (Xcc), poses a significant threat to citrus production.
• The susceptibility gene Citrus sinensis lateral organ boundary 1 (CsLOB1) is implicated in citrus canker, but its precise molecular functions remain unclear.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying CsLOB1's role in citrus response to Xcc.
• To investigate the impact of CsLOB1 manipulation on citrus susceptibility and resistance to bacterial canker.

Main Methods:

• Generation of transgenic 'wanjincheng' orange plants with CsLOB1 overexpression and RNA interference (RNAi)-mediated silencing.
• Phenotypic analysis, including growth, morphology, and canker development.
• Biochemical assays for cell wall components (pectin, cellulose, hemicellulose) and expansin accumulation.
• Transcriptome analysis (RNA-seq) and chromatin immunoprecipitation sequencing (ChIP-seq) to identify CsLOB1-regulated genes.

Main Results:

• CsLOB1 overexpression led to dwarfism, altered leaf morphology, and enhanced cell proliferation, increasing susceptibility to canker.
• RNAi-silencing of CsLOB1 enhanced resistance to canker without hindering pathogen entry.
• CsLOB1 positively regulates cell wall modification, cytokinin metabolism, and cell division, directly targeting genes in these pathways.
• Specific CsLOB1 targets include genes involved in cell wall remodeling and phytohormone signaling (cytokinin and brassinosteroid).

Conclusions:

• CsLOB1 promotes cell proliferation and citrus canker development via cell wall remodeling and phytohormone signaling.
• CsLOB1 is a key regulator of citrus susceptibility to bacterial canker.
• Targeting CsLOB1 offers a potential strategy for enhancing citrus disease resistance.