AGO2a but not AGO2b mediates antiviral defense against infection of wild-type cucumber mosaic virus in tomato

Abstract

Evolutionarily conserved antiviral RNA interference (RNAi) mediates a primary antiviral innate immunity preventing infection of broad-spectrum viruses in plants. However, the detailed mechanism in plants is still largely unknown, especially in important agricultural crops, including tomato. Varieties of pathogenic viruses evolve to possess viral suppressors of RNA silencing (VSRs) to suppress antiviral RNAi in the host. Due to the prevalence of VSRs, it is still unknown whether antiviral RNAi truly functions to prevent invasion by natural wild-type viruses in plants and animals. In this research, for the first time we applied CRISPR-Cas9 to generate ago2a, ago2b, or ago2ab mutants for two differentiated Solanum lycopersicum AGO2s, key effectors in antiviral RNAi. We found that AGO2a but not AGO2b was significantly induced to inhibit the propagation of not only VSR-deficient Cucumber mosaic virus (CMV) but also wild-type CMV-Fny in tomato; however, neither AGO2a nor AGO2b regulated disease induction after infection with either virus. Our findings firstly reveal a prominent role of AGO2a in antiviral RNAi innate immunity in tomato and demonstrate that antiviral RNAi evolves to defend against infection of natural wild-type CMV-Fny in tomato. However, AGO2a-mediated antiviral RNAi does not play major roles in promoting tolerance of tomato plants to CMV infection for maintaining health.

Acknowledgements

The authors thank professor Chuanyou Li for sharing the construct pHEE401, and Chuanlong Sun and Yuzhen Mei for experimental advice; and all members of Zhongxin Guo’s and Yanhong Han’s groups for helpful suggestions. This work was supported by the National Natural Science Foundation of China (31870146 and 32160619), the Science Foundation of Fujian province (2020 J02014), ‘Hundred Talent’ of Fujian Province, Yunnan Seed Industry Joint Laboratory (202205AR070001), and the Science and Technology Major Project of Yunnan (202202AE090022).

Author contributions

Z.X.G. and L.L.Z. designed the experiments, analyzed the data, and wrote the manuscript. Z.Z.K provided advice and support for the research. L.L.Z., Y.F.C., X.M.X., H.Y.G., and J.M.C. performed the experiments. All authors read and approved the manuscript.

Data availability

All data needed to evaluate the conclusions in the paper are present in the paper and/or the supplementary materials. All newly generated plant or vector materials are available for sharing upon request. Sequence data used in this study were downloaded from Sol Genomics (SolGenomicsNetwork). The accession numbers are as follows: AGO2a (Solyc02g069260), AGO2b (Solyc02g069270), AGO1a (Solyc06g072300), AGO1b (Solyc03g098280), AGO3 (Solyc02g069280), AGO5 (Solyc06g074730), AGO6 (Solyc07g049500), AGO10a (Solyc09g082830), AGO10b (Solyc12g006790), AGO15 (Solyc03g111760), Actin (Solyc11g005330), NtAGO2 (XM_016629769), AtAGO2 (AT1G31280), and OsAGO2 (XP_015636011).

Conflict of interest

None declared.

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