Plants, like other multicellular organisms, survive through a delicate balance between growth and defense against pathogens. Salicylic acid (SA) is a major defense signal in plants, and the perception mechanism as well as downstream signaling activating the immune response are known. Here, we identify a parallel SA signaling that mediates growth attenuation. SA directly binds to A subunits of protein phosphatase 2A (PP2A), inhibiting activity of this complex. Among PP2A targets, the PIN2 auxin transporter is hyperphosphorylated in response to SA, leading to changed activity of this important growth regulator. Accordingly, auxin transport and auxin-mediated root development, including growth, gravitropic response, and lateral root organogenesis, are inhibited. This study reveals how SA, besides activating immunity, concomitantly attenuates growth through crosstalk with the auxin distribution network. Further analysis of this dual role of SA and characterization of additional SA-regulated PP2A targets will provide further insights into mechanisms maintaining a balance between growth and defense.

• Keywords
• NPR1, PIN, PP2A, auxin, auxin transport, gravitropism, immunity, phosphorylation, protein phosphatase 2A, salicylic acid,
• MeSH
• Arabidopsis growth & development   physiology   MeSH
• Plant Immunity MeSH
• Plant Roots growth & development   metabolism   MeSH
• Salicylic Acid metabolism   MeSH
• Indoleacetic Acids metabolism   MeSH
• Protein Phosphatase 2 metabolism   MeSH
• Arabidopsis Proteins metabolism   MeSH
• Signal Transduction * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Salicylic Acid MeSH
• Indoleacetic Acids MeSH
• PIN2 protein, Arabidopsis MeSH Browser
• PP2A protein, Arabidopsis MeSH Browser
• Protein Phosphatase 2 MeSH
• Arabidopsis Proteins MeSH

Intercellular distribution of the plant hormone auxin largely depends on the polar subcellular distribution of the plasma membrane PIN-FORMED (PIN) auxin transporters. PIN polarity switches in response to different developmental and environmental signals have been shown to redirect auxin fluxes mediating certain developmental responses. PIN phosphorylation at different sites and by different kinases is crucial for PIN function. Here we investigate the role of PIN phosphorylation during gravitropic response. Loss- and gain-of-function mutants in PINOID and related kinases but not in D6PK kinase as well as mutations mimicking constitutive dephosphorylated or phosphorylated status of two clusters of predicted phosphorylation sites partially disrupted PIN3 phosphorylation and caused defects in gravitropic bending in roots and hypocotyls. In particular, they impacted PIN3 polarity rearrangements in response to gravity and during feed-back regulation by auxin itself. Thus PIN phosphorylation, besides regulating transport activity and apical-basal targeting, is also important for the rapid polarity switches in response to environmental and endogenous signals.

• MeSH
• Arabidopsis drug effects   physiology   MeSH
• Phosphorylation MeSH
• Gravitropism * MeSH
• Plant Roots drug effects   physiology   MeSH
• Indoleacetic Acids pharmacology   MeSH
• Gravity Sensing MeSH
• Cell Polarity * MeSH
• Arabidopsis Proteins genetics   metabolism   MeSH
• Plant Growth Regulators pharmacology   MeSH
• Amino Acid Sequence MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Indoleacetic Acids MeSH
• PIN3 protein, Arabidopsis MeSH Browser
• Arabidopsis Proteins MeSH
• Plant Growth Regulators MeSH