Abstract
SummaryPlants, 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.
Highlights
Life of multicellular organisms is a permanent trade-off to allocate resources between growth and defense against pathogens
Salicylic acid (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
Summary
Life of multicellular organisms is a permanent trade-off to allocate resources between growth and defense against pathogens. Salicylic acid (SA) is a classical plant hormone traditionally connected with plant immunity, and its levels increase in response to pathogen attack [1]. SA functions as an endogenous signal mediating local and systemic defense responses against pathogens by upregulating the production of pathogenesis-related (PR) proteins. Following increase in SA levels, NPR1 translocates from cytoplasm into nucleus [5,6,7], thereby allowing binding to the downstream transcription factors and regulation of the expression of downstream genes [8]. NPR1 functions as a transcriptional activator, whereas NPR3 and NPR4 are transcriptional repressors, all working independently and harmoniously to regulate the expression of downstream genes [7]
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