The roles of anion channels inArabidopsisimmunity

Abstract

Plants respond to constant challenges from microbial pathogens by employing a 2-layered innate immune system. 1 The first layer, namely pathogen-associated pattern (PAMP)-triggered immunity (PTI), is triggered by molecular patterns conserved on many types of microbes. However, adapted pathogens can secret effector proteins into host cells to suppress PTI. In turn, plants have evolved additional receptors that detect such effectors and mount a second-layer of defense, called effector-triggered immunity (ETI). 1-3Anion efflux is an early response of plant cell upon exposure to PAMPs and pathogens. [4][5][6] The activity of anion channels has been shown to be required for such responses, especially for PTI. 4,7 Recently, we reported that the product of the chloride channel gene CLCd negatively regulates PTI in Arabidopsis.8 Since AtCLCd is localized to the TGN, 9 it is not likely to be directly involved in anion flux across the plasma membrane. Patch-clamp studies have revealed the presence of Rapid-type (R-type) and Slow-type (S-type) anion channels in plants, 10,11 and inhibition of R-type anion channels in Arabidopsis suspension cells suppresses flagellin-induced ROS production. 4 However, the identity and physiological roles of the channels responsible for the anion flux are unclear.It has been shown that niflumic acid (Nif) specifically blocks R-type anion channels, whereas 4,4'-diisothiocyanatostilbene-2, 2'-disulfonic acid (DIDS) blocks S-type anion channels. 4,12 Here, these 2 blockers were used to investigate the function of anion channels in PTI and ETI in Arabidopsis seedlings. A well-studied PAMP, flg22, the 22-amino acid epitope of flagellin, was used to induce ROS bursts typical of the PTI response.13 Leaf discs of Arabidopsis were incubated in water containing 100μM of one or other anion channel blocker for 30min before adding 100nM flg22. ROS production was significantly reduced in the DIDS-treated samples, but enhanced in the Nif-treated samples (Fig. 1A). Next, we checked the effects of the anion channel blockers on another PTI response, callose deposition. Arabidopsis leaves were infiltrated with 500μM anion channel blocker one hour before exposure to 1μM flg22. In agreement with the ROS results, callose deposition was reduced by DIDS, but increased by Nif (Fig. 1B, 1C). These data indicate that the S-type anion channel promotes PTI in Arabidopsis, whereas the R-type anion channel inhibits it.ETI, which is triggered directly or indirectly by recognition of pathogen effectors by host resistance (R) proteins, is a strong defense response whose hallmark is the hypersensitive cell death response (HR) at infection sites. [1][2][3]14 To assess whether anion channels are involved in ETI, we monitored the effects of the anion channel blockers on the development of HR cell death in Arabidopsis leaves upon infection with avirulent bacteria. Leaves of 4-wk-old Arabidopsis plants were infiltrated with Pseudomonas syringae pv tomato (Pst) DC3000 carrying avrRpm1 or avrRps4. The effectors AvrRpm1 and AvrRps4 a...

DataSheet_1.docx

“…Clalso enhanced plant resistance to pathogen infection by suppressing bacterial multiplication in intercellular spaces, and this enhancement is partially dependent on the SA pathway but not PTI responses, especially those mediated by FLS2 (Figure 2). This result indicated that the mechanism by which Cltreatment enhanced disease resistance differed from that resulting from anion channel mutants or stimulated by channel inhibitors (Guo et al, 2014a(Guo et al, , 2014b. Moreover, in the absence the pathogen infection, the genes related to immune responses and defense metabolites were downregulated (Supplementary Figure S4D), which is consistent with the observation that salt treatment suppresses the SA pathway.…”

Stress-induced electrolyte leakage from root cells of higher plants: background, mechanism and physiological role

“…Недавно продемонстрирована ключевая роль быстрых (R-тип) и медленных (S-тип) анионных каналов в анионной утечке из листьев A. thaliana (L.) Heynh. при добавлении в среду бактериального элиситора flg22 [61]. Это указывает на то, что утечка электролитов при патогенном стрессе связана не только с механическим повреждением тканей, а также на то, что она может вовлекать контролируемый механизм -активацию ионных каналов.…”

Chloride salt enhances plant resistance to biotic stresses

“…For example, the chloride channel family protein CLCd can negatively regulate microbe pattern-triggered immunity (PTI), possibly via altered pH in the Golgi complex (Guo et al, 2014b). Pharmacological treatments showed that anion channels differentially participated in PTI and effector-triggered immunity (Guo et al, 2014a), but whether changing Cllevels by irrigation would affect plant biotic responses remains unclear. Yang et al (2019) found that pre-irrigation with 300 mM NaCl drastically inhibited the cell-death phenotype of acd5 mutants, which lack ceramide kinase and exhibit accelerated cell death (Liang et al, 2003).…”

“…For example, the chloride channel family protein CLCd can negatively regulate microbe pattern-triggered immunity (PTI), possibly via altered pH in the Golgi complex ( Guo et al., 2014b ). Pharmacological treatments showed that anion channels differentially participated in PTI and effector-triggered immunity ( Guo et al., 2014a ), but whether changing Cl - levels by irrigation would affect plant biotic responses remains unclear.…”