Endoplasmic reticulum KDEL-tailed cysteine endopeptidase 1 of Arabidopsis (AtCEP1) is involved in pathogen defense

Abstract

Programmed cell death (PCD) is a genetically determined process in all multicellular organisms. Plant PCD is effected by a unique group of papain-type cysteine endopeptidases (CysEP) with a C-terminal KDEL endoplasmic reticulum (ER) retention signal (KDEL CysEP). KDEL CysEPs can be stored as pro-enzymes in ER-derived endomembrane compartments and are released as mature CysEPs in the final stages of organelle disintegration. KDEL CysEPs accept a wide variety of amino acids at the active site, including the glycosylated hydroxyprolines of the extensins that form the basic scaffold of the cell wall. In Arabidopsis, three KDEL CysEPs (AtCEP1, AtCEP2, and AtCEP3) are expressed. Cell- and tissue-specific activities of these three genes suggest that KDEL CysEPs participate in the abscission of flower organs and in the collapse of tissues in the final stage of PCD as well as in developmental tissue remodeling. We observed that AtCEP1 is expressed in response to biotic stress stimuli in the leaf. atcep1 knockout mutants showed enhanced susceptibility to powdery mildew caused by the biotrophic ascomycete Erysiphe cruciferarum. A translational fusion protein of AtCEP1 with a three-fold hemaglutinin-tag and the green fluorescent protein under control of the endogenous AtCEP1 promoter (PCEP1::pre-pro-3xHA-EGFP-AtCEP1-KDEL) rescued the pathogenesis phenotype demonstrating the function of AtCEP1 in restriction of powdery mildew. The spatiotemporal AtCEP1-reporter expression during fungal infection together with microscopic inspection of the interaction phenotype suggested a function of AtCEP1 in controlling late stages of compatible interaction including late epidermal cell death. Additionally, expression of stress response genes appeared to be deregulated in the interaction of atcep1 mutants and E. cruciferarum. Possible functions of AtCEP1 in restricting parasitic success of the obligate biotrophic powdery mildew fungus are discussed.

Nuclear Function of Subclass I Actin-Depolymerizing Factor Contributes to Susceptibility in Arabidopsis to an Adapted Powdery Mildew Fungus

“…Infected-cell-specific death has been observed in the wild type attacked by adapted powdery mildew fungus (Höwing et al, 2014). The increased frequency of infected-cell-specific death and increased amplitude of PR1 induction in ADF1-4Ri appear to suggest the increased basal defense level and primed defense response in ADF1-4Ri and, possibly, in adf4.…”

Flowering conditions affect flower longevity in Syringa vulgaris and cause changes in protein content, protease activity and expression of a KDEL-CysEP gene

“…These observations and the expression pattern of To elucidate the role of cysteine endoproteases during flower senescence, genes of cysteine protease that up-regulate during flower senescence, have been cloned from the petals of Dianthus caryophyllus (Jones et al 1995), Hemerocallis (Valpuesta et al 1995;Guerrero et al 1998), Alstroemeria peruviana (Wagstaff et al 2002), Sandersonia aurantiaca (Eason et al 2002), Narcissus pseudonarcissus (Hunter et al 2007), and Gladiolus grandiflora (Arora and Singh 2004). It has been found that many of the senescence associated cysteine proteases are KDELCysEPs (Helm et al 2008;Höwing et al 2014). KDELCysEPs belong to an important group of cysteine endoproteases that are unique to plants by a characteristic C-terminal KDEL sequence directing retention in the endoplasmic reticulum (ER) (Helm et al 2008;Höwing et al 2014;Battelli et al 2014).…”

MONENSIN SENSITIVITY1 (MON1)/CALCIUM CAFFEINE ZINC SENSITIVITY1 (CCZ1)-Mediated Rab7 Activation Regulates Tapetal Programmed Cell Death and Pollen Development

“…Previous studies showed two different localization patterns of CEP1 in different tissues. CEP1 showed ER pattern in transgenic Arabidopsis roots (Höwing et al, 2014) but vacuole pattern in tapetal cells . Due to the tissue-specific localization pattern of CEP1, the possible effects of mon1 on the vacuolar transport of CEP1 in tapetum can be done in future research using transgenic Arabidopsis plants expressing GFP-tagged CEP1 driven by tapetum-specific promoter in the wild type and mon1.…”