The study revealed a new mechanism of host infection by Citrus Huanglong

Recently, the Journal of Experimental Botany published online a research paper by the team of the National Citrus Seedling Detoxification Center of the Citrus Research Institute of Southwest University, which found that the secretion protein of Citrus Huanglong disease manipulates the autophagy of host cells, thereby promoting pathogenic bacterial infection.

Citrus yellow dragon disease red nose fruit symptoms. Photo courtesy of the Citrus Research Institute of Southwest University

Citrus huanglongbing, HLB) the number one disease in the global citrus industry, mainly transmitted by citrus psyllid in the field, at present, the epidemic risk of the disease in some dominant citrus producing areas in China has intensified, and non-epidemic areas are also facing the threat of the disease, posing a severe challenge to China’s transformation from a large citrus producer to a strong country.

Citrus yellow dragon disease leaf mottled symptoms. Photo courtesy of the Citrus Research Institute of Southwest University

According to reports, citrus yellow dragon disease is an obligate parasite of phloem, which has not been able to be pure culture in vitro, which seriously restricts the process of research and development of prevention and control agents and disease resistance genetic engineering breeding.

Pathogenic bacteria can interfere with host defense responses by secreting effector proteins. The study found that transgenic citrus of Huanglong’s effector protein SDE4405 could inhibit the expression of host immune-related genes, thereby promoting the proliferation of Huanglong’s disease in citrus. Furthermore, it was found that this effector protein could interact with the ATG8 family protein, a citrus autophagy-related gene, and activate autophagy in Benthama and citrus cells.

Autophagy plays an important role in the process of removing pathogens and their pathogenic factors in plant cells, and pathogenic effector proteins play the dual role of “promoting” or “inhibiting” pathogens in regulating autophagy. In this study, the study showed that SDE4405-induced autophagy had a function favorable for bacterial infection through ATG8 gene overexpression and silencing studies. 

This study provides for the first time the molecular evidence of the use of effector proteins to regulate autophagy of host cells to promote pathogenic infection, which lays a foundation for in-depth elucidating of the regulatory mechanism of effector proteins on autophagy of host cells, thereby deeply revealing the pathogenic mechanism of Huanglongia citrus, and will also provide theoretical support for the directional improvement of citrus against Huanglong’s disease, which has important theoretical significance and application prospects. (Source: Li Chen, China Science News)                                                      

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