Plant nucleotide-binding leucine-rich repeat receptors (NLRs) regulate immunity and cell death. In Arabidopsis, a subfamily of “helper” NLRs are required by many “sensor” NLRs. Active NRG1.1 oligomerized, was enriched in plasma membrane puncta and conferred cytoplasmic Ca2+ influx in plant and human cells. NRG1.1-dependent Ca2+ influx and cell death were sensitive to Ca2+ channel blockers and were suppressed by mutations impacting oligomerization or plasma membrane enrichment. Ca2+ influx and cell death mediated by NRG1.1 and ACTIVATED DISEASE RESISTANCE 1 (ADR1), another “helper” NLR, required conserved negatively charged N-terminal residues. Whole-cell voltage-clamp recordings demonstrate that Arabidopsis “helper” NLRs form Ca2+-permeable cation channels to directly regulate cytoplasmic Ca2+ levels and consequent cell death. Thus, “helper” NLRs transduce cell death signals directly.

NCT00890708.

GDSL-type lipase is a hydrolytic enzyme whose amino acid sequence contains a pentapeptide motif (Gly-X-Ser-X-Gly) with active serine (Ser). Pepper GDSL-type lipase (CaGLIP1) gene was isolated and functionally characterized from pepper leaf tissues infected by Xanthomonas campestris pv. vesicatoria (Xcv). The CaGLIP1 protein was located in the vascular tissues of Arabidopsis root. The CaGLIP1 gene was preferentially expressed in pepper leaves during the compatible interaction with Xcv. Treatment with salicylic acid, ethylene and methyl jasmonate induced CaGLIP1 gene expression in pepper leaves. Sodium nitroprusside, methyl viologen, high salt, mannitol-mediated dehydration and wounding also induced early and transient CaGLIP1 expression in pepper leaf tissues. Virus-induced gene silencing of CaGLIP1 in pepper conferred enhanced resistance to Xcv, accompanied by the suppressed expression of basic PR1 (CaBPR1) and defensin (CaDEF1) genes. The CaGLIP1 lipase produced in Escherichia coli hydrolyzed the substrates of short and long chain nitrophenyl esters. The CaGLIP1-overexpressing Arabidopsis exhibited enhanced hydrolytic activity toward short and long chain nitrophenyl ester, as well as enhanced susceptibility to the bacterial pathogen Pseudomonas syringae pv. tomato and the biotrophic oomycete Hyaloperonospora parasitica. SA-induced expression of AtPR1 and AtGST1, also was delayed in CaGLIP1-overexpressing plants by SA application. During seed germination and plant growth, the CaGLIP1 transgenic plants showed drought tolerance and differential expression of drought- and abscisic acid (ABA)-inducible genes AtRD29A, AtADH and AtRab18. ABA treatment differentially regulated seed germination and gene expression in wild-type and CaGLIP1 transgenic Arabidopsis. Overexpression of CaGLIP1 also regulated glucose- and oxidative stress signaling. Together, these results indicate that CaGLIP1 modulates disease susceptibility and abiotic stress tolerance.

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