The plant cuticle regulates apoplastic transport of salicylic acid during systemic acquired resistance

Abstract

The plant cuticle is often considered a passive barrier from the environment. We show that the cuticle regulates active transport of the defense hormone salicylic acid (SA). SA, an important regulator of systemic acquired resistance (SAR), is preferentially transported from pathogen-infected to uninfected parts via the apoplast. Apoplastic accumulation of SA, which precedes its accumulation in the cytosol, is driven by the pH gradient and deprotonation of SA. In cuticle-defective mutants, increased transpiration and reduced water potential preferentially routes SA to cuticle wax rather than to the apoplast. This results in defective long-distance transport of SA, which in turn impairs distal accumulation of the SAR-inducer pipecolic acid. High humidity reduces transpiration to restore systemic SA transport and, thereby, SAR in cuticle-defective mutants. Together, our results demonstrate that long-distance mobility of SA is essential for SAR and that partitioning of SA between the symplast and cuticle is regulated by transpiration.

The glycosyltransferase UGT76B1 is critical for plant immunity as it governs the homeostasis ofN-hydroxy-pipecolic acid

“…Here, the authors showed that SAG was hydrolyzed in the apoplast to SA and that rather SA than SAG entered the cell. In addition, other studies support our notion that both NHP and SA are mobile between local and systemic tissue in Arabidopsis and tobacco (Yalpani et al, 1991;Chen et al, 2018;Lim et al, 2020). Nevertheless, it is still a matter of debate, as there was also evidence presented that SA is not the mobile signal for SAR (Vernooij et al, 1994b;Vernooij et al, 1994a).…”

Systemic propagation of immunity in plants

“…Similarly, cuticle‐defective Arabidopsis mutants, which display impaired apoplastic SA accumulation and transport, accumulate SAR signals in petiole exudates of infected leaves, but do not respond with SAR to petiole exudates of infected wild‐type plants (Fig. 1) (Xia et al ., 2009; Lim et al ., 2020). Notably, Lim et al .…”

“…et al (1994);Lim et al (2020) C. Wenig et al(2019) Jung et al (2009); Gao et al (2014); Lim et al (2016); Wenig et al (2019) Park et al (2007, 2009) Y. Wang et al (2018); Wenig et al (2019) Riedlmeier et al (2017);Wenig et al (2019) Chanda et al (2011); Wenig et al (2019) Jung et al (2009); Cecchini et al (2015) Maldonado et al Signaling functions of systemic acquired resistance (SAR) signaling components in local SAR signal generation/transmission and systemic SAR signal perception/propagation. Signaling components are listed in groups of potentially co-operating signals and assigned to phloem-mediated (green arrow) and airborne (pink arrow) routes.…”

More stories to tell: NONEXPRESSOR OF PATHOGENESIS‐RELATED GENES1, a salicylic acid receptor

“…In contrast, two other SAR-associated chemical signals, glycerol-3-phosphate (G3P) and azelaic acid (AzA), are transported preferentially via plasmodesmata (Lim et al, 2016). More interestingly, Lim et al (2020) recently showed that transport of SA from local to distal tissues is essential for SAR, and the transportation is governed by water potential in the infected tissue (Figure 1). Indeed, reduced water potential preferentially routes SA to cuticle wax rather than to the apoplast in cuticle-defective mutants (Lim et al, 2020).…”