Alfalfa benefits fromMedicago truncatula: TheRCT1gene fromM. truncatulaconfers broad-spectrum resistance to anthracnose in alfalfa

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Abstract
Alfalfa is economically the most important forage legume worldwide. A recurrent challenge to alfalfa production is the significant yield loss caused by disease. Although knowledge of molecular mechanisms underlying host resistance should facilitate the genetic improvement of alfalfa, the acquisition of such knowledge is hampered by alfalfa's tetrasomic inheritance and outcrossing nature. However, alfalfa is congeneric with the reference legumeMedicago truncatula, providing an opportunity to useM. truncatulaas a surrogate to clone the counterparts of many agronomically important genes in alfalfa. In particular, the high degree of sequence identity and remarkably conserved genome structure and function between the two species enablesM. truncatulagenes to be used directly in alfalfa improvement. Here we report the map-based cloning ofRCT1, a host resistance (R) gene inM. truncatulathat confers resistance to multiple races ofColletotrichum trifolii, a hemibiotrophic fungal pathogen that causes anthracnose disease of alfalfa.RCT1is a member of the Toll-interleukin-1 receptor/nucleotide-binding site/leucine-rich repeat (TIR-NBS-LRR) class of plantRgenes and confers broad-spectrum anthracnose resistance when transferred into susceptible alfalfa plants. Thus,RCT1provides a novel resource to develop anthracnose-resistant alfalfa cultivars and contributes to our understanding of host resistance against the fungal genusColletotrichum. This work demonstrates the potential of usingM. truncatulagenes for genetic improvement of alfalfa.