ABA-CsABI5-CsCalS11 module upregulates Callose deposition of citrus infected with .

Huanglongbing (HLB) primarily caused by Liberibacter asiaticus (Las) has been threatening citrus production globally. Under HLB conditions, an excessive accumulation of the polysaccharide callose in citrus phloem occurs, leading to phloem blockage and starch accumulation in leaves. The callose production is controlled by callose synthases (CalS), which have multiple members within plants. However, the knowledge of callose production in the citrus upon infection with Las is limited. In this study, we firstly identified 11 in the genome through bioinformatics and found the expression pattern of exhibited a positive correlation with callose deposition in Las-infected leaves (correlation coefficient of 0.77,  ≤ 0.05). Knockdown of resulted in a reduction of callose deposition and starch accumulation in Las-infected citrus. Interestingly, we observed significantly higher concentrations of abscisic acid (ABA) in HLB-infected citrus leaves compared to uninfected ones. Furthermore, the expressions of , , and in the ABA pathway substantially increased in citrus leaves upon Las infection. Additionally, the expression of was significantly upregulated in citrus leaves following the application of exogenous ABA. We confirmed that CsABI5, a pivotal component of the ABA signaling pathway, regulates expression by binding to its promoter using yeast one-hybrid assay, dual luciferase assay, and transient expression in citrus leaves. In conclusion, our findings strongly suggest that the CsABI5-CsCalS11 module plays a crucial role in regulating callose deposition through the ABA signaling pathway during Las infection. The results also revealed new function of the ABA signaling pathway in plants under biotic stress.