The bacterial quorum sensing signal DSF hijacksArabidopsis thalianasterol biosynthesis to suppress plant innate immunity

Abstract

36Quorum sensing (QS) is a recognized phenomenon that is crucial for regulating population-37 related behaviors in bacteria. However, the direct specific effect of QS molecules on host biology is 38 largely under-studied. In this work, we show that the QS molecule DSF (cis-11-methyl-dodecenoic acid) 39 produced by Xanthomonas campestris pv. campestris can suppress pathogen-associated molecular 40 pattern (PAMP)-triggered immunity (PTI) in Arabidopsis thaliana, mediated by flagellin-induced activation 41 of flagellin receptor FLS2. The DSF-mediated attenuation of innate immunity results from the alteration of 42 oligomerization states and endocytic internalization of plasma membrane FLS2. DSF altered the lipid 43 profile of Arabidopsis, with a particular increase of the phytosterol species, which impairs the general 44 endocytosis pathway mediated by clathrin and FLS2 nano-clustering on the plasma membrane. The DSF 45 effect on receptor dynamics and host immune responses could be entirely reversed by sterol removal. 46Together, our results highlighted the importance of sterol homeostasis to plasma membrane organization 47 and demonstrate a novel mechanism by which pathogenic bacteria use their communicating molecule to 48 manipulate PAMP-triggered host immunity. 49 50 Keywords: quorum sensing, plasma membrane, endocytosis, plant-pathogen interaction 51 52 SIGNIFICANCE STATEMENT 53Bacteria rely on small signalling molecules called quorum sensing (QS) signals to communicate 54 and coordinate their behaviors. QS is known to regulate gene expression, production of virulence factors, 55 and biofilm formation for pathogenic bacteria to effectively colonize their hosts and cause diseases. In this 56 work, we found a class of QS molecule called diffusible-signal factor (DSF), produced by devastating 57 phytopathogenic bacteria such as Xanthomonas spp. and Xylella fastidiosa, could communicate directly 58 with plant host and subvert plant innate immunity by inducing plant sterol production and thereby, 59 attenuating receptor signalling through hindering the receptor clustering and plant endocytosis. The 60 results significantly enrich our understanding of the mechanisms in the tug-of-war between bacterial 61 pathogenesis and host immunity. 62 63 infection (4). The 3OC12-HSL was also shown to be recognized by the bitter taste receptor, T2R family 73 protein, T2R38 in neutrophils, lymphocytes and monocytes to activate innate immune responses (5). 74Similarly, plant pathogenic bacteria also secrete small-molecule virulence factors to cross-talk with host 75 and manipulate host immunity during infection. QS molecules produced by several bacterial 76 phytopathogens showed a wide range of interference in host development and defence mechanisms, 77including the root morphological development in an auxin-dependent manner or callose deposition during 78 immune responses (6-8). However, the detailed mechanisms of how QS molecules directly influence 79 plant host development and pathology, especially the PAMP-mediated host immunity,...

Salicylic acid regulates PIN2 auxin transporter hyperclustering and root gravitropic growth via Remorin‐dependent lipid nanodomain organisation in Arabidopsis thaliana

“…Steroid hormone brassinosteroid (BR) promotes the partitioning of the BR receptor Brassinosteroid Insensitive 1 (BRI1) to membrane nanodomains that in turn stimulates BRI1 internalisation in response to BR (Wang et al ., 2015). The modulation of the nanoclustering of receptor Flagellin Sensing 2 (FLS2) on the plant cell surface fine tunes the flagellum‐mediated innate immune responses under different conditions during plant–bacteria communication (Cui et al ., 2018; Gronnier et al ., 2020; Tran et al ., 2020). Despite both immune receptor FLS2 and the growth receptor BRI1 forming nanoclusters on the cell surface, they distribute within distinct nanodomains, suggesting a spatial separation within the PM when responding to developmental or defence signals (Bucherl et al ., 2017).…”

Formin nanoclustering-mediated actin assembly during plant flagellin and DSF signaling

“…DSF-stimulated cellulose production might be enhanced by an increase in sitosterol-glucoside, which has been proposed as a primer for cellulose biosynthesis (Peng et al, 2002) or via the enhanced activities of CESA complex by increasing its surface participation into sterol-enriched nanodomains. Consistent with the second speculated scenario, multiple sterol mutants have previously exhibited striking deficiencies in cellulose production (Schrick et al, 2004) and DSF consequences (Tran et al, 2020). Several outstanding questions for actin assembly in plant innate immunity remain to be addressed in future studies, such as how distinct host responses on the CW-PM-AC continuum crosstalk with each other, synergistically or antagonistically, for actin remodeling during plant immune responses.…”

“…34, 108884, March 30, 2021 11 Article ll OPEN ACCESS Wiskott-Aldrich syndrome protein (WASP) and Arp2/3 nucleator complex have been reported as underpinning mechanisms in regulating actin nucleation upon immune-cell activation, by tuning the mobility, stoichiometry, and dwell times of the WASP-Arp2/3 complex on the PM (Case et al, 2019b;Padrick et al, 2011;Su et al, 2016). Recently, the nanoscale organization of several important cell-surface biomolecules has been suggested for tuning signal transductions, including the remorin clustering for modulating PM compartmentalization (Gronnier et al, 2017;Huang et al, 2019;Jaillais and Ott, 2020;Jarsch et al, 2014), PRR clustering for PTI signaling (B€ ucherl et al, 2017;Tran et al, 2020), Rho of Plants6 (ROP6) nanoclustering for Rho GTPase signaling (Platre et al, 2019). Because the resting state of biomolecules might also influence the valency increase caused by VF-triggered signaling activation, a fusion using monomeric fluorescent protein would be best for concluding the exact status of protein oligomerization, although the tendency toward a multivalency increase could be similar.…”

“…The steady-state anisotropy measurement of Arabidopsis surface fluorescent molecules by VA-TIRFM has been stated in the previous study (Tran et al, 2020). Briefly, to quantify the steady-state anisotropy of AtFH6-GFP, the instrument G-Factor was first determined by calculating the ratio of I pa and I pe emission intensities of free FITC solution, which was imaged using the same microscope setting as for AtFH6-GFP.…”

“…campestris (Xcc), diffusible signal factor (DSF) (Brock et al, 2010;Chatterjee et al, 2008;Newman et al, 2004;Yang et al, 2017). DSF showed multifaceted effects, including regulation of bacterial invasion in plants by controlling other VFs (Kalappurakkal et al, 2019;Ryan et al, 2015) and an increase in phytosterol production of plant hosts (Tran et al, 2020). Although flagelin and DSF were found to remodel Arabidopsis AC differently, both of them used a convergent mechanism for reorganizing AC, namely fine tuning of formin nanoclustering on the PM.…”