Breakthrough in citrus disease resistance: LasLYS2 gene offers dual protection against huanglongbing and citrus canker

Citrus diseases, such as Huanglongbing (HLB) and citrus canker caused by Candidatus Liberibacter asiaticus (CaLas) and Xanthomonas citri pv. citri (Xcc) respectively, pose significant threats to the global citrus industry, causing billions in losses with no effective cure available. Recent research has focused on endolysins from bacteriophages as a potential solution for developing disease resistance. These endolysins, known for their specificity and rapid bactericidal activity, have shown promise in other agricultural applications. However, the challenge remains in applying this approach to citrus diseases, as HLB resistance has not yet been identified in the Citrus genus and most cultivars are susceptible to canker.

In August 2023, Horticulture Research published a research entitled by “An endolysin gene from Candidatus Liberibacter asiaticus confers dual resistance to huanglongbing and citrus canker”.

Initially, the bactericidal activity of LasLYS1 and LasLYS2 was tested in vitro using the Oxford cup, as both proteins selectively inhibited certain bacterial strains. LasLYS2 exhibited broader bactericidal activity and showed substantial inhibitory effects against Xcc, the pathogen responsible for citrus canker, at higher concentrations. In vivo, LasLYS1 and LasLYS2 were introduced into Carrizo citrange via Agrobacterium-mediated transformation, thereby enhancing HLB resistance with LasLYS2 transgenic plants exhibiting higher resistance. Furthermore, LasLYS2 also conferred significant resistance to citrus canker, unlike LasLYS1, which only showed weak resistance.

The study also examined the impact of LasLYS1 and LasLYS2 on the endophytic bacterial community in plants through 16S rRNA deep sequencing. It was observed that these endolysins significantly altered the root microbiome of transgenic plants, affecting populations of several bacterial families, including Xanthomonadaceae and Rhizobiaceae. Interestingly, an increase in beneficial bacteria like Burkholderiaceae and Rhodanobacteraceae was noted, suggesting a favorable shift in the microbial community for disease resistance. Additionally, the study revealed significant upregulation of genes associated with plant hormone signaling, plant-pathogen interaction, and the MAPK signaling pathway. This suggests that LasLYS1 and LasLYS2 have both bactericidal effects and impact on the plant innate immune response. Comparative analysis of LasLYS1 and LasLYS2 sequences found that LasLYS2, which lacks a domain present in LasLYS1, has more potent bactericidal activity.

In conclusion, the study provided strong evidence that LasLYS2, in particular, can be an effective tool for breeding citrus plants with enhanced resistance to both HLB and citrus canker. This dual resistance marks a significant advance in combating these devastating citrus diseases.

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References

Authors

Lanzhen Xu^†, Kaiqing Mo^†, Danlu Ran, Juanjuan Ma, Lehuan Zhang, Yijia Sun, Qin Long, Guojin Jiang, Xiaochun Zhao^*, and Xiuping Zou^*

†Contributed equally to this work.

Affiliations

Integrative Science Center of Germplasm Creation in Western China (CHONGQING) Science City, Citrus Research Institute, Southwest University/National Citrus Engineering Research Center, Chongqing 400712, China

About Xiaochun Zhao & Xiuping Zou

Xiaochun Zhao: He is deputy director of Citrus Research Institute, Chinese Academy of Agricultural Sciences. His research focuses on molecular breeding for citrus.

Xiuping Zou: He is a Professor at Citrus Research Institute, Chinese Academy of Agricultural Sciences. His research area is molecular breeding for citrus resistance to disease.