Wheat curl mite (WCM, Aceria tosichella Keifer) causes significant wheat yield losses in many wheat-growing regions worldwide. It not only rolls leaves to directly disrupt wheat growth, more importantly it transmits a devastating, widespread virus to cause wheat streak mosaic virus (WSMV) disease. Cmc4 is a WCM resistance gene from Aegilops tauschii and provides high WCM resistance when it was transferred into wheat.

By sequencing a Cmc4-containing Ae. tauschii accession using PacBio HiFi technology, map-based cloning, and conducting genome-wide association and gene expression studies, we successfully identified two candidate genes in the Cmc4 interval. Transformation of the candidate genes confirmed a CC-NB-LRR gene regulating Cmc4 resistance to WCM

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Comparison of the numbers and sizes of mites and their eggs on the infested leaves between Cmc4 near-isogenic lines found that the Cmc4 conferred WCM resistance by disrupting mite growth that resulted in death of most mites and production of only a few eggs in the Cmc4-resistant plants.

Analysis of geographic distribution of Cmc4-carrying accessions suggested Central Asia as the most likely origin of Cmc4. Diagnostic markers have been developed for selection of Cmc4 in wheat breeding programs. Cloning of Cmc4 is an essential step toward understanding the wheat-mite interactions and cloning of other Cmc genes for genetic control of both WCM and WSMV in wheat.