Genome-wide discovery of Pichia galeiformis-secreted proteins and their induction of green mold resistance in citrus fruit

Microbe-secreted proteins could alter plant defense systems, but yeast-secreted proteins and their impact on plant disease resistance remains uninvestigated. As our team had previously found that Pichia galeiformis (P. galeiformis) induced citrus green mold resistance, the purpose of this study was to identify its secreted proteins and their role in disease resistance. The genome of P. galeiformis was completely sequenced, and 4386 putative protein-coding genes were identified. The crude culture of P. galeiformis contained 1443 proteins. Among these proteins, 55 were identified as secreted proteins with an N-terminal signal peptide and lacking transmembrane structural domain. Overexpression of secreted proteins 2-gene0581, 22-gene0896, 23-gene0290, 12-gene3564, 9-gene0639, and 15-gene0649 significantly reduced citrus fruit disease incidence and lesion diameter. And the best effect was achieved by 15-gene0649 treatment. Notably, P. galeiformis 15-gene0649, which was named PgSCP, encoded a novel protein. The purified protein PgSCP demonstrated considerable ability to prevent green mold caused by Penicillium digitatum in citrus. This study presented here confirms that yeast could increase citrus green mold resistance through secreted proteins. Those secreted proteins offer a fresh insight for controlling postharvest disease in citrus fruit as well as a new commercialization and application method for antagonistic yeast.