Pepper mild mottle virus coat protein interacts with pepper chloroplast outer envelope membrane protein OMP24 to inhibit antiviral immunity in plants

Abstract

Pepper mild mottle virus (PMMoV) is a devastating viral pathogen of pepper ( Capsicum annuum) but it is unclear whether and how peppers protect against PMMoV infection. The expression of the chloroplast outer membrane protein 24 (OMP24) of C. annuum was upregulated under PMMoV infection and it interacted with PMMoV coat protein (CP). Silencing of OMP24 in either C. annuum or Nicotiana benthamiana facilitated PMMoV infection, whereas overexpression of N. benthamiana OMP24 in transgenic plants inhibited PMMoV infection. Both C. annuum OMP24 (CaOMP24) and N. benthamiana OMP24 (NbOMP24) localized to the chloroplast and have a moderately hydrophobic transmembrane domain that is necessary for their localization. Overexpression of CaOMP24 induced stromules, perinuclear chloroplast clustering, and accumulation of reactive oxygen species (ROS), the typical defense responses of chloroplasts transferring the retrograde signaling to the nucleus to regulate resistance genes. The expression of PR1 and PR2 was also upregulated significantly in plants overexpressing OMP24. Self-interaction of OMP24 was demonstrated and was required for OMP24-mediated plant defense. Interaction with PMMoV CP interfered with the self-interaction of OMP24 and impaired OMP24-induced stromules, perinuclear chloroplast clustering and ROS accumulation. The results demonstrate the defense function of OMP24 in pepper during viral infection and suggest a possible mechanism by which PMMoV CP modulates the plant defense to facilitate viral infection.

Acknowledgements

We thank Prof. M.J. Adams, Minehead, UK for correcting the English of the manuscript. This work was financially supported by National Key R&D Program of China (2022YFD1401200), China Agriculture Research System of MOF and MARA (CARS-24-C-04), National Natural Science Foundation of China (32270294), Ningbo Major Special Projects of the Plan ‘Science and Technology Innovation 2025’ (2021Z106), the Postdoctoral Science Foundation of Anhui Province, China (2021B558) and K.C. Wong Magna Fund in Ningbo University.

Author contributions

F.Y., K.H., R.Q., J.P. and J.C. designed the project. K.H., Ho.Z., D.Y., Hu.Z., Z.J., and Y.Z. performed experiments. K.H., F.Y., J.W., Y.L., G.W. and S.R. analysed data and reviewed the manuscript. K.H. and F.Y. wrote the paper.

Data availability

All relevant data are available within the article and its supplementary materials.

Conflict of interest

The authors declare that they have no competing interests.

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