AUTHOR=Zhang Mian , Feng Hao , Zhao Yuhuan , Song Linlin , Gao Chen , Xu Xiangming , Huang Lili 

TITLE=Valsa mali Pathogenic Effector VmPxE1 Contributes to Full Virulence and Interacts With the Host Peroxidase MdAPX1 as a Potential Target

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.00821

DOI=10.3389/fmicb.2018.00821

ISSN=1664-302X

ABSTRACT=<p>The <italic>Valsa</italic> canker, caused by <italic>Valsa mali</italic> (<italic>V. mali</italic>), is a destructive disease of apple in Eastern Asia. Effector proteins are important for fungal pathogenicity. We studied a candidate effector VmPxE1 isolated based on the genome information of <italic>V. mali.</italic> By using the yeast invertase secretion assay system, VmPxE1 was shown to contain a signal peptide with secretory functions. VmPxE1 can suppress BCL-2-associated X protein (BAX)-induced cell death with a high efficacy of 92% in <italic>Nicotiana benthamiana</italic>. The expression of <italic>VmPxE1</italic> was upregulated during the early infection stage and deletion of <italic>VmPxE1</italic> led to significant reductions in virulence on both apple twigs and leaves. VmPxE1 was also shown to target an apple ascorbate peroxidase (MdAPX1) by the yeast two-hybrid screening, bimolecular fluorescence complementation and <italic>in vivo</italic> co-immunoprecipitation. Sequence phylogenetic analysis suggested that MdAPX1 was an ascorbate peroxidase belonging to a subgroup of heme-dependent peroxidases of the plant superfamily. The ectopic expression of <italic>MdAPX1</italic> in the mutant of <italic>VmPxE1</italic> significantly enhanced resistance to H<sub>2</sub>O<sub>2</sub>, while the presence of <italic>VmPxE1</italic> seems to disturb <italic>MdAPX1</italic> function. The present results provide insights into the functions of VmPxE1 as a candidate effector of <italic>V. mali</italic> in causing apple canker.</p>