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<p>Small peptides (SPs) are critical signaling molecules that regulate a wide array of biological processes in plants, including growth, development, and immune responses. However, their specific roles in the interaction between citrus and <i>Candidatus</i> Liberibacter asiaticus (<i>C</i>Las), the causal agent of the devastating huanglongbing (HLB) disease, remain largely unexplored. This study presents a comprehensive genome-wide identification and characterization of SPs in <i>Citrus sinensis</i>. We identified 5,854 transcripts encoding SPs, constituting 11.81% of the total annotated transcripts. Through comparative transcriptome analysis, we identified 422 SPs that were differentially expressed upon <i>C</i>Las infection, with 217 being up-regulated and 205 down-regulated. Bioinformatic analyses revealed that these responsive SPs are involved in key biological processes such as hormone signaling, plant-pathogen interaction, and immune response activation. A focused screen for small secretory peptides (SSPs) among the up-regulated SPs led to the identification of several members of the Phytosulfokine (PSK) family, including CsPSK1, CsPSK2, and CsPSK4, as prominent HLB-responsive candidates. We experimentally validated that these CsPSKs are secreted into the apoplast, a critical interface for plant-pathogen interactions. Functional characterization through virus-induced gene silencing (VIGS) of the PSK homolog in <i>Nicotiana benthamiana</i> resulted in compromised resistance to <i>Pseudomonas syringae</i>. Conversely, transient overexpression of <i>CsPSK1</i>, <i>CsPSK2</i>, and <i>CsPSK4</i> in <i>C. sinensis</i> significantly enhanced resistance to <i>Xanthomonas citri</i> subsp. <i>citri</i> (<i>Xcc</i>). These findings collectively demonstrate that CsPSKs are positive regulators of plant immunity and play a conserved role in defense against bacterial pathogens. Furthermore, this research provides insights into the molecular functions of SPs in citrus defense and identifies CsPSKs as potential targets for further investigation in HLB management.</p>

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The impact of CsPSKs on plant immunity: insights from a genome-wide study of small peptides in Citrus sinensis

  • 期刊论文

  • 发表日期：

    2026年1月21日

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  • Yanan Hu,
  • Ye Chen,
  • Along Qiu,
  • Ruimin Li,
  • Guiyan Huang

摘要

Small peptides (SPs) are critical signaling molecules that regulate a wide array of biological processes in plants, including growth, development, and immune responses. However, their specific roles in the interaction between citrus and Candidatus Liberibacter asiaticus (CLas), the causal agent of the devastating huanglongbing (HLB) disease, remain largely unexplored. This study presents a comprehensive genome-wide identification and characterization of SPs in Citrus sinensis. We identified 5,854 transcripts encoding SPs, constituting 11.81% of the total annotated transcripts. Through comparative transcriptome analysis, we identified 422 SPs that were differentially expressed upon CLas infection, with 217 being up-regulated and 205 down-regulated. Bioinformatic analyses revealed that these responsive SPs are involved in key biological processes such as hormone signaling, plant-pathogen interaction, and immune response activation. A focused screen for small secretory peptides (SSPs) among the up-regulated SPs led to the identification of several members of the Phytosulfokine (PSK) family, including CsPSK1, CsPSK2, and CsPSK4, as prominent HLB-responsive candidates. We experimentally validated that these CsPSKs are secreted into the apoplast, a critical interface for plant-pathogen interactions. Functional characterization through virus-induced gene silencing (VIGS) of the PSK homolog in Nicotiana benthamiana resulted in compromised resistance to Pseudomonas syringae. Conversely, transient overexpression of CsPSK1, CsPSK2, and CsPSK4 in C. sinensis significantly enhanced resistance to Xanthomonas citri subsp. citri (Xcc). These findings collectively demonstrate that CsPSKs are positive regulators of plant immunity and play a conserved role in defense against bacterial pathogens. Furthermore, this research provides insights into the molecular functions of SPs in citrus defense and identifies CsPSKs as potential targets for further investigation in HLB management.