Journal club: resistance to wheat disease through recognition of a protein

Introduction: Wheat yellow rust disease
Every year large wheat crop losses are caused by wheat yellow rust disease, a disease on wheat caused by the fungus Puccinia striiformis f. sp. tritici (Pst). This fungus is not able to make all plant species sick: Nicotiana benthamiana, a relative of tobacco and a much studied species, is resistant to it. This plant is resistant because it can recognize the fungus and activate an immune response. Understanding how this plant recognizes the invading fungus and thus becomes resistant will increase our chance of ever breeding a resistant wheat variety that is also resistant to this fungus.

Results: Recognition of a protein is the key to a resistant plant
In their paper, Dagvadorj and colleagues show that N. benthiamiana recognizes a small protein secreted by the fungus. Recognition of this protein results in the expression of genes that lead to the activation of defense responses in the plant. The defense responses result in reduced disease symptoms after pathogen attack. Future studies identifying the receptor on the plant cells that recognizes PstSCR1 will therefore provide material to improve disease resistance against a range of pathogens.

For the enthusiasts: How did the researchers get these results?
This paper follows up on another paper published in 2009 that looked among all the genes of Puccinia striiformis f. sp. tritici for genes that are expressed when the fungus is infecting a plant. They found fifteen genes that encode secreted proteins and end their paper with ‘[t]hese genes are candidates for further studies to determine their functions in wheat-Pst interactions.’

Dagvadorj and colleagues performed just such a study. Their study focuses on one of the fifteen genes, one that codes for PstSCR1, as a possible explanation for the resistance of N. benthiamiana to Pst. They first check whether PstSCR1 mRNA is produced when the fungus infects wheat. This is the case from 72 h to 8 days post infection. Next, they checked the effect of PstSCR1 on plant immunity. To do this, they expressed PstSCR1 on N. benthiama leaves before putting pathogens on the leaves. The infection, as measured by the lesion diameter on the plant or the number of spores produced by the pathogen, is reduced in leaves with PstSCR1 expression. One possible explanation for the reduced infection is activation of the plant immune response. To test this, the researchers checked mRNA levels of genes involved in the plant immune response after infiltration of the leaves by purified PstSCR1. Both defense genes that were checked, NbACRE31 and NbCYP71D20, were indeed activated by PstSCR1. Thus, the detection of this protein results in the activation of the plant immune response, which in turn results in resistance against the pathogen secreting the protein.

Discussed paper
Dagvadorj B, Ozketen AC, Andac A, Duggan C, Bozkurt TO, Akkaya MS (2017) A Puccinia sriiformis f. sp. tritici secreted protein activates plant immunity at the cell surface. Scientific reports 7: 1141
DOI: 10.1038/s41598-017-01100-z

Paper that precedes this one:
Yin C, Chen X, Wang X, Han Q, Kang Z, Hulbert SH (2009) Generation and analysis os expression sequence tags from haustoria of the wheat strpe rust fungus Puccinia striiformis f. sp. Tritici. BMC Genomics  10: 626

Disclaimer: blog posts in the category ‘journal club’ are not intended to cover the whole paper discussed. Instead, I discuss the parts that I think are most interesting for a general public. I try my utmost to prevent any mistakes in these blogs, I apologize in advance for any mistakes that I make anyway.

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