ABA-CsABI5-CsCalS11 module upregulates Callose deposition of citrus infected with Candidatus Liberibacter asiaticus

Abstract

Huanglongbing (HLB) primarily caused by Candidatus Liberibacter asiaticus (CLas) 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 CLas is limited. In this study, we firstly identified 11 CalSs in the Citrus sinensis genome through bioinformatics and found the expression pattern of CsCalS11 exhibited a positive correlation with callose deposition in CLas-infected leaves (correlation coefficient of 0.77, P ≤ 0.05). Knockdown of CsCalS11 resulted in a reduction of callose deposition and starch accumulation in CLas-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 CsABI5, CsPYR, and CsSnRK2 in the ABA pathway substantially increased in citrus leaves upon CLas infection. Additionally, the expression of CsCalS11 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 CsCalS11 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 CLas infection. The results also revealed new function of the ABA signaling pathway in plants under biotic stress.

Acknowledgements

The manuscript has been revised based on feedback from Prof. Changyong Zhou at Southwest University, Prof. Yiwen Deng at CAS Center for Excellence in Molecular Plant Sciences, and peer reviewers. We express our gratitude to them. The project is financially supported by the National Key R&D Program of China (No. 2021YFD140080), Chongqing Natural Science Foundation (CSTB2023NSCQ-MSX0519), and Earmarked Funds for the China Agriculture Research System (CARS-26).

Author contributions

L.Y., Z.S., and S.C. conceived and designed this research. X.G., J.S., Q.Z., M.L., and H.X. experimented. L.Y., Q.Z., and Y.H. analyzed the data. L.Y., Z.S., Q.L., and X.Z. wrote and modified the manuscript. All authors involved in this study read and approved the manuscript.

Conflict of interest statement

The authors have no conflict of interest to declare.

Data availability

The data that support the findings are available within the article and supplementary data.

Supplementary Data

Supplementary data is available at Horticulture Research online.

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