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A study led by Professor Liu Zhiyun from the Institute of Genetics and Developmental Biology (IGDB) of the Chinese Academy of Sciences in partnership with international groups and published in the Plant Biotechnology Journal points the way to developing more resilient wheat varieties and reducing the need for pesticides.
Scientists identified two genes associated with wheat nucleotides and possessing repetitive leucines (NLR), RXL and Pm5e. They provide resistance to the dangerous wheat disease powdery mildew, according to a press release from the Chinese Academy of Sciences compiled by Zhang Nannan.
Most cloned genes providing resistance to powdery mildew encode CNL (CC-NLR) proteins. One such protein is Sr35, present in wheat. It can form a wheel-shaped pentameric complex known as a resistosome, in which the coiled-coil plasma membrane domain (CC) acts as a channel for Ca2+ ions. This leads to the influx of Ca2+ ions, triggering immune responses.
In most cases, a single NLR protein is capable of simultaneously recognizing pathogen effector molecules and initiating an immune response. However, some NLRs function in pairs, where one, known as the sensor NLR, recognizes pathogen effectors through its integrated domain, and the other, an executive NLR or helper NLR, is responsible for initiating the immune response.
Such NLR pairs are often adjacent to each other in the genome. For example, this is observed in rice with the pairs RGA4/RGA5 and Pik-1/Pik-2, as well as in Arabidopsis with the pairs RPS4/RRS1. However, it is still unknown whether these pairs of NLRs function in enhancing wheat disease resistance.
As a result of their research, Liu and his colleagues from Sainsbury (UK), Nanjing Normal University, and Henan University of Science and Technology demonstrated the cooperation of the RXL and Pm5e genes in wheat, providing resistance to powdery mildew. Both genes encode atypical NLR proteins: RXL contains a shortened NB-ARC domain, while Pm5e has an atypical CC domain.
Additional research showed that RXL and Pm5e preferentially form heteromeric complexes, and the CC domain of Pm5e can competitively interact to specifically suppress the hypersensitive reaction induced by the CC domain of RXL. This allows us to propose a possible regulatory mechanism for this NLR pair.
"We establish that two closely related NLR genes, RXL and Pm5e, oriented in parallel, function together as an NLR pair providing wheat resistance to powdery mildew. The resistance role of the RXL/Pm5e pair was confirmed by mutagenesis, gene suppression, and genetic analysis," the study authors report.
This study represents the first evidence that NLR pairs play an important role in wheat disease resistance. It elucidates the RXL/Pm5e molecular mechanism regulating wheat resistance to powdery mildew and provides genetic resources for understanding powdery mildew resistance and wheat breeding.
Overall, the study was comprehensive, using a rigorous methodology of cloning and testing the RXL/Pm5e pairs.
