Abstract
SUGARWIN1 and 2 are defense proteins from sugarcane. Their gene expression is known to be induced in response to wound and Diatraea saccharalis damage. Although the recombinant SUGARWIN protein does not affect insect development, it promotes significant morphological and physiological changes in Fusarium verticillioides and Colletotrichum falcatum, which lead to fungal cell death via 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. Our results show that SUGARWINs play an important role in plant defense against opportunistic pathogens. We demonstrated that SUGARWINs are induced by C. falcatum, and the induction of SUGARWINs can vary among sugarcane varieties. The sugarcane variety exhibiting the highest level of SUGARWIN induction exhibited a considerable reduction in C. falcatum infection. Furthermore, SUGARWIN1 exhibited ribonuclease, chitosanase, and chitinase activity, whereas SUGARWIN2 exhibited only chitosanase activity. This variable enzymatic specificity seems to be the result of divergent amino acid composition within the substrate-binding site.
Highlights
The plant defense system is under constant selective pressure to improve its response to pathogens and insect damage (Cui et al, 2002; Medeiros et al, 2016)
We identified two insect-induced genes homologous to BARWIN in sugarcane, called SUGARWIN1 and SUGARWIN2
We found that SUGARWIN genes are induced at different levels by D. saccharalis depending on the sugarcane variety (Figure 1)
Summary
The plant defense system is under constant selective pressure to improve its response to pathogens and insect damage (Cui et al, 2002; Medeiros et al, 2016). Pathogen recognition by plants activates the host defense response, resulting in cell wall fortification via callose and lignin synthesis, the production of secondary metabolites such as phytoalexins that exhibit an antimicrobial effect, and the accumulation of pathogenesis-related proteins (PR proteins) (Pieterse and van Loon, 1999). The pathogenesis-related protein-4 (PR-4) family is a group of proteins equipped with a BARWIN-like domain. This domain can be associated with a chitin-binding domain, well known as the hevein-like domain. This association separates the family into PR4 classes I (with the hevein-like domain) and II (without the hevein-like domain) (Broekaert et al, 1990; Neuhaus et al, 1996).
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