Salicylic acid-induced alkalinization of the apoplast requires TRANSMEMBRANE KINASE 1 and results in growth attenuation

Abstract

The phytohormone salicylic acid (SA) has a key role in regulating plant growth and stress response. In the past, most of the growth-related SA functions have been explained by crosstalk with the master growth regulator auxin. By affecting polarity of auxin transporters, SA changes auxin distribution in the root and inhibits growth of the main root and activates lateral root formation. However, only recently there is evidence emerging that SA impacts growth processes independently of nuclear auxin signalling, possessing yet unknown mechanistic functions. Here we show that SA activity depends on TRANSMEMBRANE KINASE 1 (TMK1) resulting in apoplast alkalinization and growth restriction. SA treatment prevents phosphorylation and activation of plasma membrane (PM) H+-ATPases at the cell surface and does not depend on the auxin receptor Auxin Binding Protein 1 (ABP1). We suggest that alkalinization of the apoplast by SA serves as mechanism to balance stress response and growth.