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<p>Citrus Huanglongbing (HLB), caused by <i>Candidatus</i> Liberibacter asiaticus (<i>C</i>Las), severely affects citrus growth and nutrient balance. However, the relationships among growth inhibition, mineral redistribution, and zinc transporter-related responses in HLB-infected ‘Newhall’ navel orange remain unclear. This study aimed to clarify the effects of HLB on plant growth, organ-specific mineral nutrient distribution, and the expression of zinc transporter-related genes in ‘Newhall’ navel orange grafted onto trifoliate orange rootstock. Healthy and HLB-infected grafted seedlings were grown under greenhouse conditions for nine months. <i>C</i>Las infection was confirmed by PCR. Plant growth, biomass accumulation, and root morphology were measured. Mineral element concentrations in leaves, stems, and roots were determined by ICP-MS (Inductively Coupled Plasma MassSpectrometry). The expression of representative zinc transporter-related genes was analyzed by qRT-PCR in different tissues. Compared to healthy controls, HLB infection significantly impaired plant growth and disrupted nutrient homeostasis. Infected plants exhibited marked reductions in stem diameter, biomass accumulation, and chlorotic, misshapen leaf development, alongside consistent declines in root morphology and function—evidenced by reduced root length, surface area, and nutrient uptake capacity. Mineral nutrient distribution across leaves, stems, and roots was dysregulated, with organ-specific redistribution of mineral nutrients, with decreased P (phosphorus), K (potassium), and Ca (calcium) in leaves but significant Ca accumulation in stems and roots. In parallel, HLB triggered tissue-specific transcriptional changes in zinc transporter-related genes, including increased <i>ZIP1</i> expression in roots, increased <i>HMA2</i> and <i>HMA4</i> expression in stems, and increased <i>HMA1</i> and <i>MTP3</i> expression in leaves. HLB suppressed plant growth and altered mineral homeostasis in ‘Newhall’ navel orange, and these changes were accompanied by tissue-specific regulation of zinc transporter-related genes. The results suggest that transcriptional adjustment of zinc uptake, transport, and compartmentation may represent an adaptive response linking HLB-induced nutrient imbalance with plant physiological adjustment. Collectively, this study provides a mechanistic foundation for optimizing nutrient management in HLB-affected orchards, integrating genetic responses and agronomic interventions to mitigate citrus decline.</p>

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The Effects of Citrus Huanglongbing on the Mineral Nutrients and Zinc Transport Gene Expression in ‘Newhall’ Navel Orange

  • 期刊论文

  • 发表日期：

    2026年7月29日

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  • Guan Guan,
  • Si Zhang,
  • Jingyuan Xu,
  • Jing Zhu

摘要

Citrus Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus (CLas), severely affects citrus growth and nutrient balance. However, the relationships among growth inhibition, mineral redistribution, and zinc transporter-related responses in HLB-infected ‘Newhall’ navel orange remain unclear. This study aimed to clarify the effects of HLB on plant growth, organ-specific mineral nutrient distribution, and the expression of zinc transporter-related genes in ‘Newhall’ navel orange grafted onto trifoliate orange rootstock. Healthy and HLB-infected grafted seedlings were grown under greenhouse conditions for nine months. CLas infection was confirmed by PCR. Plant growth, biomass accumulation, and root morphology were measured. Mineral element concentrations in leaves, stems, and roots were determined by ICP-MS (Inductively Coupled Plasma MassSpectrometry). The expression of representative zinc transporter-related genes was analyzed by qRT-PCR in different tissues. Compared to healthy controls, HLB infection significantly impaired plant growth and disrupted nutrient homeostasis. Infected plants exhibited marked reductions in stem diameter, biomass accumulation, and chlorotic, misshapen leaf development, alongside consistent declines in root morphology and function—evidenced by reduced root length, surface area, and nutrient uptake capacity. Mineral nutrient distribution across leaves, stems, and roots was dysregulated, with organ-specific redistribution of mineral nutrients, with decreased P (phosphorus), K (potassium), and Ca (calcium) in leaves but significant Ca accumulation in stems and roots. In parallel, HLB triggered tissue-specific transcriptional changes in zinc transporter-related genes, including increased ZIP1 expression in roots, increased HMA2 and HMA4 expression in stems, and increased HMA1 and MTP3 expression in leaves. HLB suppressed plant growth and altered mineral homeostasis in ‘Newhall’ navel orange, and these changes were accompanied by tissue-specific regulation of zinc transporter-related genes. The results suggest that transcriptional adjustment of zinc uptake, transport, and compartmentation may represent an adaptive response linking HLB-induced nutrient imbalance with plant physiological adjustment. Collectively, this study provides a mechanistic foundation for optimizing nutrient management in HLB-affected orchards, integrating genetic responses and agronomic interventions to mitigate citrus decline.