The Role of SUGARWIN Proteins in Sugarcane Defense Against Pathogens

In sugarcane fields, colonization of the stalk by opportunistic fungi usually occurs after Diatraea saccharalis caterpillar attacks. Plants respond to pathogens and insect attack by inducing and accumulating a large set of defense proteins. We identified two homologues of a barley wound-inducible protein (BARWIN) in sugarcane, which were designated SUGARWIN1 and 2 (sugarcane wound-inducible proteins). Although BARWIN function has not been fully established, antifungal properties have been described for a number of homologues. SUGARWIN1 and 2 gene expression are induced in response to wound, methyl jasmonate treatment and Diatraea saccharalis damage. However, the recombinant SUGARWIN protein does not affect insect development, but it promotes significant morphological and physiological changes in Fusarium verticillioides and Colletotrichum falcatum, which lead to fungal cell death by apoptosis. In this study, we deepen our understanding of the role of SUGARWINs in plant defense and the molecular mechanisms by which these proteins affect fungi by elucidating their molecular targets. We demonstrated that SUGARWINs induction can vary between sugarcane varieties and can also be induced by C. falcatum. The sugarcane variety exhibiting highest level of SUGARWINs induction exhibited a considerable reduction in C. falcatum infection. Furthermore, SUGARWIN1 exhibited ribonuclease and chitinase activity, whereas SUGARWIN2 exhibited only chitinase activity. This variable enzymatic specificity seems to be result of divergent amino acid composition within the substrate-binding site that was demonstrated by protein modeling.  Our results show that SUGARWINs play an important role in plant defense against opportunistic pathogens and can be important to red rot disease control.