Spore germination-enhancing effect on Botrytis elliptica driven by the N-terminal region of anti-fungal protein LsGRP1

LsGRP1 is a plant class II glycine-rich defense-related protein located in the cell surface of epidermis and vascular tissue of lily leaves. The LsGRP1 content appears fluctuated during Botrytis elliptica infection. Previous study demonstrated that in vitro treatment with high concentration of the N-terminal region of LsGRP1 (LsGRP1N) slightly enhanced the spore germination of B. elliptica but inhibited or did not alter the spore germination of other tested pathogenic fungi and bacterial growth (Lin et al., 2014). Moreover, LsGRP1 exhibited greater inhibitory activity on B. elliptica than LsGRP1C did (Pan, 2015), suggesting that LsGRP1N may facilitate the anti-B. elliptica effect of LsGRP1C. Thus, in this study, the effect of LsGRP1N on B. elliptica was dissected to improve the knowledge of antimicrobial activity of LsGRP1. In this research, in vitro assay showed that LsGRP1N conducted earlier spore germination and enhanced early hyphal growth of B. elliptica. When SUMO-LsGRP1N fusion protein was infiltrated into lily leaves before inoculation with B. elliptica, higher fungal biomass and more severe host cell death occurred as compared with the control treatment of SUMO partner of fusion protein. Further assay revealed that LsGRP1 did not conduct plant cell death, the enhanced growth of B. elliptica triggered by SUMO-LsGRP1N was likely a cause of higher extent of plant cell death. In addition, in vitro treatment of equal-length peptide with identical amino acid composition of LsGRP1N (LsGRP1N-iaac) did not affect spore germination and early hyphal growth of B. elliptica, the possibility of LsGRP1N simply as a nutrient supplement was excluded. On the other hand, spores of B. elliptica in germinating stage were more sensitive to LsGRP1C as compared with that of un-germinated ones, and a combination of LsGRP1N and LsGRP1C conducted stronger inhibitory effect than the sole treatment of LsGRP1C did. Thus, the N-terminal region of LsGRP1 on cell surface of lily leaf triggering earlier spore germination of B. elliptica and conducting germinating spores vulnerable to LsGRP1C, which then capable of reducing the population of B. elliptica and diminishing symptom development were persumed.