.Apple vacuolar processing enzyme 4 is regulated by cysteine protease inhibitor and modulates fruit disease resistance.
Abstract
Ring rot is a destructive apple disease caused by Botryosphaeria dothidea. The resistance mechanism of apple plants to B. dothidea remains unclear. Here, we show that APPLE VACUOLAR PROCESSING ENZYME 4 (MdVPE4) is involved in resistance to B. dothidea. MdVPE4 silencing reduced fruit disease resistance, whereas its overexpression improved resistance. Gene expression analysis revealed that MdVPE4 influenced the expression of fruit disease resistance-related genes, such as APPLE POLYGALACTURONASE 1 (MdPG1), APPLE POLYGALACTURONASE INHIBITOR PROTEIN 1 (MdPGIP1), APPLE ENDOCHITINASE 1 (MdCHI1), and APPLE THAUMATIN-LIKE PROTEIN 1 (MdTHA1). The expression of the four genes responding to B. dothidea infection decreased in MdVPE4-silenced fruits. Further analysis demonstrated that B. dothidea infection induced MdVPE4 expression and enzyme activation in apple fruits. Moreover, MdVPE4 activity was modulated by apple cysteine proteinase inhibitor 1 (MdCPI1), which also contributed to resistance towards B. dothidea, as revealed by gene overexpression and silencing analysis. MdCPI1 interacted with MdVPE4 and inhibited its activity. However, MdCPI1 expression was decreased by B. dothidea infection. Taken together, our findings indicate that the interaction between MdVPE4 and MdCPI1 plays an important role in modulating fruit disease resistance to B. dothidea.
Apple ring rot caused by Botryosphaeria dothidea is an essential and prevalent disease in the apple orchard in China. Our previous study demonstrated that dimethyl trisulfide (DT) from Chinese leek (Allium tuberosum) significantly suppressed the mycelial growth of B. dothidea, and inhibited the incidence of apple ring rot at postharvest. However, the mechanism underlying the inhibitory role of DT against B. dothidea is not fully understood. Comparing the control and the DT-treated B. dothidea mycelia transcriptomes revealed that a heat shock protein 20 (Hsp20) strongly responded to DT treatment. This study identified four Hsp20 genes throughout the B. dothidea genome (BdHsp20_1-4). Each BdHsp20 had an ACD conserved domain with a variable N-terminal region and a short C-terminal extension. The segmental duplication event has contributed to the expansion of the BdHsp20 gene family. Compared to the wildtype strain, the CRISPR/Cas9-edited BdHsp20 mutant (ΔBdHsp20) decreased the mycelial growth by 55.95% and reduced the disease symptom on postharvest apple fruit by 96.34%. However, the BdHsp20 complemented strain (ΔBdHsp20_C) significantly restored the growth and pathogenicity, which suggested that the BdHsp20 gene was closely involved in the growth and pathogenicity of B. dothidea. This study would accelerate the exploration of the molecular mechanism of the inhibitory effect of DT against B. dothidea and also provide new insights for the management of apple ring rot disease.
Courtesy,
Yonghong Huang
Junping Liu
Jinghui Li
Meng Sun
Yanxin Duan1
College of Horticulture, Qingdao Agricultural University, China.
ORIGINAL RESEARCH article.
Thanks to, Frontiers Media S.A.
Microbe and Virus Interactions with Plants
doi: 10.3389/fmicb.2022.930012
