Priming effect of menadione sodium bisulphite against salinity stress in Arabidopsis involves epigenetic changes in genes controlling proline metabolism

Plants are able to develop numerous defence strategies to face stress. Amongst these, higher plants are capable of demonstrating stress imprint, a mechanism related with the phenomenon of priming. This is usually defined as genetic or biochemical modifications induced by a first stress exposure that leads to enhanced resistance to a later stress. Menadione sodium bisulphite (MSB), a water-soluble addition compound of vitamin K3, was first studied as a plant growth regulator and has been later widely shown to function as plant defence activator against several pathogens in a number of plant species. We recently reported that treating Arabidopsis seeds with MSB primes salt tolerance by inducing an early acclimation to salt stress. Here we describe the analysis of the effect of MSB on cytosine methylation in a salt stress background demonstrating that one of the mechanisms underlying this early acclimation to salt stress is an epigenetic mark. Specifically, MSB leads to a hypomethylation state at the promoter region of genes involved in the biosynthesis (P5CS1) and degradation (ERD5) of proline, affecting mainly CHG and CHH sites(where H is any nucleotide except G). The epigenetic changes detected are correlated with the observed expression patterns of P5CS1 (upregulation) and ERD5 (downregulation) genes and the increase in proline accumulation.