ИСТИНА

Introduction: It is known that individual defence-related genes show different levels of mRNA accumulation in leaves and roots when measured before and after encountering pathogens. The purpose of our work was to investigate the mechanism for controlling the stability of the mRNA of the Nicotiana benthamiana Kunitz peptidase inhibitor-like (NbKPIL) gene, which is abundant in the roots but can only be detected in the leaves of this plant after pathogen attack. Results: Unlike silencing, which is associated with nucleotide-specific mRNA degradation, the stability of NbKPIL mRNA is determined by the expression of an alternative ORF encoding an amphipathic 53-aa (53-aa aORF) polypeptide (53aa-pep). The expression of 53-aa aORF is performed from the maternal NbKPIL mRNA, which provides the synthesis of both proteins detected in the cell wall membranes. The expression of 53-aa aORF cannot be explained by the existence of a cryptic promoter in the NbKPIL gene. The activity of chloroplasts is a prerequisite for the expression of 53-aa aORF. Prolonged exposure of plants to darkness sharply increases the content of NbKPIL mRNA, and the return of plants to light restores the NbKPIL mRNA content to the original level. Removing the start codon from 53-aa aORF also dramatically increases the maternal mRNA content in the leaves. The stability of NbKPIL mRNA is determined not by the expression of 53-aa aORF from NbKPIL mRNA per se but by the amphipathic properties of the 53aa-pep. The introduction of mutations in the NbKPIL-encoding sequence cancelling the ability of the 53aa-pep to bind to membranes increases NbKPIL mRNA content in the leaves. Conclusions: The low content of NbKPIL mRNA in the leaves of an intact plant is determined by the chloroplast-regulated synthesis of the amphipathic 53aa-pep. Acknowledgements: The work was supported by the grant of the President of the Russian Federation MD-5697.2016.4 and the RFBR grant 16-34-00062_mol_a.