Metabolome Analyses Provides Insights into Fruit Symptom Development Caused By Huanglongbing in Citrus reticulata Blanco cv. Wokan

Citrus Huanglongbing (HLB), caused by the phloem-limited bacterium ‘Candidatus Liberibacter asiaticus’ (CLas), is the most devastating diseases threatening citrus production worldwide. Infected fruit exhibited lopsided morphology and color inversion (‘Red-nose’ fruit), but the underlying mechanisms remain unclear. Here, we investigated the dynamic CLas-host interactions associated with fruit symptom development through integrated transcriptomic and metabolomic analyses of fruit pith and pericarp from 30 to 240 days after flowering (DAF). “Red-nose” symptoms appeared at 180 DAF and intensified as CLas titers peaked at 240 DAF. CLas transcriptomes profiling revealed that the early colonization (30–90 DAF) was characterized by upregulated genes involved in proliferation, nutrient uptake, stress tolerance and secretion systems, while later stages (180–240 DAF) showed broad downregulation of core metabolism with sustained transporter and surface‑structure gene expression. CLas infection shifted host metabolism by enhancing sucrose degradation, reducing sucrose synthesis, disrupting auxin/cytokinin pathways, and perturbing pigment pathways. Host defense metabolites were depleted early (30/90 DAF) but accumulated during ripening (180/240 DAF). These findings revealed how CLas temporally manipulated host growth and defense, driving HLB‑associated fruit disorders.