Results from this study explored the inhibitory effect of RHO1 gene (GenBank accession number KY859864) from the antagonistic yeast, Cryptococcus laurentii ZJU10, on the control of Penicillium expansum in pear fruit and its possible mechanism involved. The RHO1 gene was successfully cloned and overexpressed in Saccharomyces cerevisiae. Sequence analysis showed high similarity with Rho family proteins, implying a primary role of Rho1 in the cell wall integrity (CWI) signaling pathway. Gene expression of RHO1 and other five CWI-related genes (including Pkc1, Rlm1, Fks1, Fks2 and Chs3) were significant up-regulated in the treatment of SC/Rho1-induced strain (Saccharomyces cerevisiae transformed with RHO1 and induced by galactose). Meanwhile, SC/Rho1-induced treatment reduced about 61.5% of disease incidence and almost 5-times lower lesion diameter compared to the control. In addition, the growth of transformed strains was slightly lower in contrast to the wild Saccharomyces cerevisiae and the induction of fruit resistance was significantly enhanced, which was tightly linked with triggering stronger host defensive responses by priming activation. This is the first study that Rho1 has a potential function of suppressing fungal disease in harvested fruit by activating CWI signaling pathway and indicates an alternative strategy for postharvest disease management.

The study investigated the effect of autoclaved yeast on the control of blue mold in pear fruit and the possible mechanisms involved. The results demonstrated that autoclaved yeast Rhodosporidium paludigenum could stimulate remarkable resistance to the blue mold caused by Penicillium expansum in pear fruit. Autoclaved yeast had no direct antifungal activity against P. expansum in vitro and in vivo while it reduced germination of P. expansum in fruit wounds after 24 h of treatment. Moreover, the activities of four defense-related enzymes (including superoxide dismutase, catalase, peroxidase and phenylalanine ammonia-lyase) and the four pathogenesis-related protein genes (including PR1-like, endoglucanase9, endochitinase-like and PR4) were significantly enhanced and the lipid peroxidation was highly inhibited in the treatment with autoclaved yeast, which was closely related to the mechanism by which autoclaved yeast reduce the blue mold rot in pear fruit. The results from this study provides the basis for further research on the antagonistic mechanism of biocontrol yeasts in induced resistance of harvested fruit.

Auxin is a vital plant growth regulator and can also take a part in plant defense. The study focused on the efficacy of the major active form of auxin, indole-3-acetic acid (IAA), on inhibition of blue mold rot caused by Penicillium expansum in pear fruit wounds and the possible action mechanisms involved. Results indicated that IAA at 100-500 mu g mL(-1) significantly enhanced the resistance of pear fruit against blue mold rot when the treating interval was between 24 and 48 h, while it had no direct andfungal activities towards P. expansum in vitro. Moreover, IAA induced a significant increase on the activities of beta-1,3-glucanase (GLU), chitinase (CHI) and phenylalanine ammonia-lyase (PAL) in pear fruit. Furthermore, the data revealed that the expressions of endoglu9, CHI4, PR1, PR4 and PAL were up-regulated substantially in pear fruit treated with IAA. The all findings highlight the efficiency of IAA on inducing the natural resistance of pear fruit against P. expansum and suggest that the mechanisms may be closely related to the elicitation of defense-related enzymes and genes.