PbrChiA: a key chitinase of pear in response to Botryosphaeria dothidea infection by interacting with PbrLYK1b2 and down-regulating ROS accumulation

Abstract

Pear ring rot, caused by the pathogenic fungi Botryosphaeria dothidea, seriously affects pear production. While the infection-induced reactive oxygen species (ROS) burst of infected plants limits the proliferation of B. dothidea during the early infection stage, high ROS levels can also contribute to their growth during the later necrotrophic infection stage. Therefore, it is important to understand how plants balance ROS levels and resistance to pathogenic B. dothidea during the later stage. In this study, we identified PbrChiA, a glycosyl hydrolases 18 (GH18) chitinase-encoding gene with high infection-induced expression, through a comparative transcriptome analysis. Artificial substitution, stable overexpression, and virus induced gene silencing (VIGS) experiments demonstrated that PbrChiA can positively regulate pear resistance as a secreted chitinase to break down B. dothidea mycelium in vitro and that overexpression of PbrChiA suppressed infection-induced ROS accumulation. Further analysis revealed that PbrChiA can bind to the ectodomain of PbrLYK1b2, and this interaction suppressed PbrLYK1b2-mediated chitin-induced ROS accumulation. Collectively, we propose that the combination of higher antifungal activity from abundant PbrChiA and lower ROS levels during later necrotrophic infection stage confer resistance of pear against B. dothidea.

Acknowledgements

This work has been supported by the National Key Research and Development Program of China (2018YFD1000300), the National Science Foundation of China (31872070; 32072538), Fundamental Research Funds for the Central Universities (JCQY201901), the Earmarked Fund for China Agriculture Research System (CARS- 28), the Jiangsu Agriculture Science and Technology Innovation Fund (SCX(22)3215). Bioinformatic analysis was supported by the Bioinformatics Center of Nanjing Agricultural University. We also thank Dr Jianming Zeng (University of Macau), and all the members of his bioinformatics team, biotrainee, for generously sharing their experience and codes.

Author contributions

Q.C. and H.D. conceived and designed the experiments. Q.C. and X.H. carried out the experimental design. Q.L. and X.Q. helped to analyse raw sequencing data and H.Y. helped to draft the manuscript. Q.C. and H.D. managed the tissue cultures and pear seedling and performed the related experiment. Q.C. and Z.X. wrote the manuscript. X.S. and K.Q. contributed experimental materials. Z.X. and S.Z. managed the research and experiments.

Data availability

All data generated or analysed during this study are included in this published article and its supplementary information files. All of the required sequence files and annotation files of Chinese white pear were obtained from the Nanjing Agricultural University pear genome project website (http://peargenome.njau. edu.cn) [49]. The raw data that support the findings of this study have been deposited into CNGB Sequence Archive (CNSA: https:// db.cngb.org/cnsa/) [50] of China National GeneBank DataBase (CNGBdb: https://db.cngb.org/) [51] with the project number CNP0003911.

Conflict of interest statement

The authors declare no conflict of interests.

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