A better mousetrap to guard against anthracnose disease in bean

Authors: Cannon, Steven; INNES, ROGER - Indiana University

Submitted to: Journal of Experimental Botany
Publication Type: Review Article
Publication Acceptance Date: 4/1/2021
Publication Date: 5/4/2021
Citation: Cannon, S.B., Innes, R.W. 2021. A better mousetrap to guard against anthracnose disease in bean. Journal of Experimental Botany. 72(10):3487-3488. https://doi.org/10.1093/jxb/erab146.
DOI: https://doi.org/10.1093/jxb/erab146

Interpretive Summary: Crop plants face biological challenges from many sources, such as viruses, bacteria, fungi, and insects. Understanding how plants defend against these attacks is important in helping plant breeders to breed more disease resistant and robust crops. It has been known for several decades that plants employ certain "resistance genes" that recognize pathogen or insect attacks and trigger defense responses. However, there has been a persistent puzzle about these genes (and the associated proteins): how can a limited number of such genes and proteins recognize the great variety of pathogens and other attackers - which are typically also able to evolve more rapidly than their plant hosts? This "insight article" discusses a new discovery of a trick that helps broaden plants' defensive repertoire. The trick described in this case is that the plant (a bean variety) produces a "decoy" protein, which the pathogen (a fungus) attacks. The attack triggers recognition and response by the plant. The decoy protein functions something like cheese in a mouse trap: the function of the "cheese" (the plant's decoy protein) is simply to attract the "mouse" (the fungus), whereupon the "trap" (the recognition protein) responds. Understanding of this molecular mechanism of plant defense against a fungal pathogen will help breeders to develop improved bean varieties, by using this particular disease resistance gene in breeding projects. The general understanding of this defensive mechanism will also help in development of disease resistant varieties of other crops, through identification of similar classes of defensive decoy molecules in those crops.

Technical Abstract: This article comments on Richard et al. (2021), "A common bean truncated CRINKLY4 kinase controls gene-for-gene resistance to the fungus Colletotrichum lindemuthianum," which reports the identification of the Co-x disease resistance gene in common bean. The Co-x gene confers resistance against a highly virulent strain of the fungus Colletotrichum lindemuthianum. This fungus causes the disease anthracnose, which produces watery lesions on stems, leaves, pods, and seeds, and can cause up to 100% yield loss in bean, as well as many other pulse crops. Co-x confers resistance specifically to C. lindemuthianum strain 100, to which the majority of cultivated bean varieties are susceptible; so finding effective resistance genes is of high practical importance. Surprisingly, Co-x does not encode a protein similar to any known family of disease resistance proteins. Instead, it encodes a truncated, chimeric CRINKLY4 kinase. The authors argue that this protein may function as a decoy that activates the plant’s immune responses upon modification by a yet-to-be identified effector secreted by C. lindemuthianum strain 100. If so, this would represent one of the first examples of decoy-mediated recognition of a fungal effector.