Growth gene mutations open the back door for citrus canker bacteria

Recently, The Plant Journal published online the latest results from the Citrus Research Institute of Southwest University.

"Growth genes" cause citrus disease

The origin of citrus susceptibility genes is a family of genes involved in the regulation of plant growth and development.

Chen Shanchun, the corresponding author of the paper and a researcher at the National Citrus Variety Improvement Center of the Citrus Research Institute of Southwest University, told reporters that citrus-susceptible genes belong to the family of LBD transcription factors.

Healthy Fruit Photo courtesy of Zou Xiuping

However, previous studies have found that the citrus susceptibility genes derived from the growth gene family are closely related to the infection of the citrus canker pathogen Xcc.

"Xcc pathogen infection can cause pathological proliferation, swelling and necrosis of host cells.

Chen Shanchun introduced that Xcc regulates the development of citrus canker symptoms by secreting type III effectors.

The corresponding author of the paper and associate researcher of the National Citrus Variety Improvement Center of the Citrus Research Institute of Southwest University, Zou Xiuping, introduced that mutations in citrus-susceptible genes can enhance citrus canker resistance.

"As a member of the LBD family, the function of the citrus susceptibility gene in citrus growth and development is not clear, and its molecular mechanism for regulating the development of citrus canker has yet to be resolved.

Provide "food" for germs

Lanjin orange is susceptible to citrus canker.

The evaluation of canker disease resistance showed that overexpression of citrus susceptible genes significantly enhanced the susceptibility of transgenic plants to canker disease; RNAi interference with citrus susceptible genes significantly enhanced the canker resistance of transgenic plants.

After 4 years of greenhouse phenotype observation, they found that overexpression of citrus-susceptible genes resulted in a dwarf phenotype with clusters of buds and increased branches.

Zou Xiuping said that microdissection observations revealed that the above phenotype is caused by excessive cell proliferation, especially the excessive proliferation of sponge tissue cells.

And “the sponge tissue of citrus leaves is the main part of the parasitism and feeding of canker bacteria.

Gain an inch: cause host cell necrosis

In addition, they also found that citrus susceptibility genes are involved in the late stage of canker development, that is, the necrosis process of host cells.

It turns out that citrus-susceptible genes promote cell division and proliferation by positively regulating cell wall remodeling, especially the demultimerization of pectin and the accumulation of elongating proteins, cytokinin metabolism, and brassinolide signal transduction.

In addition to citrus susceptibility genes, Zou Xiuping told reporters that they also discovered the mechanism by which citrus transcription factor CsWRKY22 promotes citrus susceptibility to canker.

"Citrus transcription factor CsWRKY22 promotes citrus susceptibility to ulcer disease by regulating the expansion of host cells.
" Zou Xiuping said, and CsWRKY22 can directly act on the W-box element on the promoter of citrus susceptible genes to activate its expression.

Chen Shanchun said that these findings suggest that there is a synergistic mechanism between the pathogen PthA4 effector and the host's citrus susceptibility gene and CsWRKY22 to regulate the proliferation, expansion and necrosis of the host cell to promote the infection and spread of the pathogen.
(Source: China Science News Li Chen)

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