The Mechanosensitive Ion Channel MSL10 Modulates Susceptibility toPseudomonas syringaeinArabidopsis thaliana

Abstract

Plants sense and respond to molecular signals associated with the presence of pathogens and their virulence factors. Mechanical signals generated during pathogenic invasion may also be important, but their contributions have rarely been studied. Here we investigate the potential role of a mechanosensitive ion channel, MscS-Like (MSL)10, in defense against the bacterial pathogen Pseudomonas syringae in Arabidopsis thaliana. We previously showed that overexpression of MSL10-GFP, phospho-mimetic versions of MSL10, and the gain-of-function allele msl10-3G all produce dwarfing, spontaneous cell death, and the hyperaccumulation of reactive oxygen species. These phenotypes are shared by many autoimmune mutants and are frequently suppressed by growth at high temperature in those lines. Here, we found that the same was true for all three MSL10 hypermorphs. In addition, we show that the SGT1/RAR1/HSP90 co-chaperone complex was required for dwarfing and ectopic cell death, PAD4 and SID2 were partially required, and the immune regulators EDS1 and NDR1 were dispensable. All MSL10 hypermorphs exhibited reduced susceptibility to infection by P. syringae strain Pto DC3000, Pto DC3000 expressing the avirulence genes avrRpt2 or avrRpm1, but not Pto DC3000 hrpL, and showed an accelerated induction of PR1 expression compared to wild-type plants. Null msl10-1 mutants were delayed in PR1 induction and displayed modest susceptibility to infection by COR-deficient Pst. Finally, stomatal closure was reduced in msl10-1 loss-of-function mutants in response to Pst COR−. These data show that MSL10 modulates pathogen responses and begin to address the possibility that mechanical signals are exploited by the plant for pathogen perception.

Unbiased proteomic and forward genetic screens reveal that mechanosensitive ion channel MSL10 functions at ER-plasma membrane contact sites in Arabidopsis thaliana

“…EMS-induced suppressor mutants, referred to as s uppressed d eath from m sl10-3G ( sdm ), were initially isolated based on increased height compared to parental msl10-3G plants in the M1 and M2 generations. As msl10-3G plants share some of the characteristics of lesion-mimicking-mutants (Basu et al, 2021), and intragenic mutations are particularly common in suppressor screens of lesion-mimicking mutants (van Wersch et al, 2016), we sequenced MSL10 exons in all 40 mutant lines. Indeed, 35 had a missense mutation in the MSL10 coding or splice-junction sequences ( Figure 4-figure supplement 1a ).…”

“…The mechanosensitive ion channel MSL10 has been well studied using electrophysiological approaches (Haswell et al, 2008; Maksaev and Haswell, 2012; Maksaev et al, 2018). Genetic analyses have attributed a variety of roles to MSL10, like the induction of Ca 2+ transients, reactive oxygen species accumulation, enhanced immune responses, and programmed cell death (Basu and Haswell, 2020; Moe-Lange et al, 2021; Basu et al, 2021), but we lack a clear understanding of how MSL10 activation leads to these downstream signaling outcomes. Studies using multiple gain-of-function MSL10 alleles found that MSL10 signaling can trigger cell death independently of ion flux (Veley et al, 2014; Zou et al, 2016; Maksaev et al, 2018; Basu et al, 2020), though it remains unknown how this occurs.…”

“…MSL10 also contributes to systemic electrical and Ca 2+ signaling in response to wounding (Moe-Lange et al, 2021). MSL10 gain-of-function alleles lead to constitutive growth retardation and ectopic cell death (Basu et al, 2020) through a pathway that requires the immune co-chaperone SGT1b/RAR1/HSP90 complex, although this is likely far downstream of MSL10 activation (Basu et al, 2021). Earlier events in signal transduction by MSL10 remain unknown.…”

Calcium channels and transporters: Roles in response to biotic and abiotic stresses

“…Plant cells sense mechanical stimuli in nature, such as touch, gravity, and the stretching of membranes. MECHANOSENSITIVE (MS) ion channels that serve to sense and respond to changes in membrane tension have been known to directly couple mechanical stimuli to ion flux (Peyronnet et al, 2014;Basu and Haswell, 2017). There are a few plant MS channel families that have been reported as Ca 2+ channels (Basu and Haswell, 2017).…”

“…MECHANOSENSITIVE (MS) ion channels that serve to sense and respond to changes in membrane tension have been known to directly couple mechanical stimuli to ion flux (Peyronnet et al, 2014;Basu and Haswell, 2017). There are a few plant MS channel families that have been reported as Ca 2+ channels (Basu and Haswell, 2017). One of them is ECHANOSENSITIVE CHANNEL OF SMALL CONDUCTANCE (MSCS)-LIKE CHANNELs (MSLs).…”