RESUMO
Plant genomes encode a unique group of papain-type Cysteine EndoPeptidases (CysEPs) containing a KDEL endoplasmic reticulum (ER) retention signal (KDEL-CysEPs or CEPs). CEPs process the cell-wall scaffolding EXTENSIN (EXT) proteins that regulate de novo cell-wall formation and cell expansion. Since CEPs cleave EXTs and EXT-related proteins, acting as cell-wall-weakening agents, they may play a role in cell elongation. The Arabidopsis (Arabidopsis thaliana) genome encodes 3 CEPs (AtCPE1-AtCEP3). Here, we report that the genes encoding these 3 Arabidopsis CEPs are highly expressed in root-hair (RH) cell files. Single mutants have no evident abnormal RH phenotype, but atcep1-3 atcep3-2 and atcep1-3 atcep2-2 double mutants have longer RHs than wild-type (Wt) plants, suggesting that expression of AtCEPs in root trichoblasts restrains polar elongation of the RH. We provide evidence that the transcription factor NAC1 (petunia NAM and Arabidopsis ATAF1, ATAF2, and CUC2) activates AtCEPs expression in roots to limit RH growth. Chromatin immunoprecipitation indicates that NAC1 binds to the promoter of AtCEP1, AtCEP2, and, to a lower extent, AtCEP3 and may directly regulate their expression. Inducible NAC1 overexpression increases AtCEP1 and AtCEP2 transcript levels in roots and leads to reduced RH growth while the loss of function nac1-2 mutation reduces AtCEP1-AtCEP3 gene expression and enhances RH growth. Likewise, expression of a dominant chimeric NAC1-SRDX repressor construct leads to increased RH length. Finally, we show that RH cell walls in the atcep1-3 atcep3-2 double mutant have reduced levels of EXT deposition, suggesting that the defects in RH elongation are linked to alterations in EXT processing and accumulation. Our results support the involvement of AtCEPs in controlling RH polar growth through EXT processing and insolubilization at the cell wall.
Assuntos
Proteínas de Arabidopsis , Arabidopsis , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Regulação da Expressão Gênica de Plantas , Peptídeo Hidrolases/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
Lumazine synthase from Brucella spp. (BLS) is a highly immunogenic decameric protein. It is possible to insert foreign peptides or proteins at its ten-amino acid termini. These chimeras elicit systemic and oral immunity without adjuvants, which are commonly needed in the formulation of subunit-based vaccines. Here, we show that BLS induces the cross presentation of a covalently attached peptide OVA(257-264) and a specific cytotoxic response to this peptide in the absence of adjuvants. Unlike other subunit-based vaccines, this chimera induces rapid activation of CTLs and a specific cytotoxic response, making this polymeric protein an ideal antigen carrier for vaccine development. Adoptive transfer of transgenic OT-I T cells revealed efficient cross presentation of BLS-OVA(257-264)in vivo. BLS-OVA(257-264) immunization induced the proliferation of OVA(257-264)-specific CD8+ lymphocytes and also increased the percentage of OVA(257-264)-specific CD8+ cells expressing the early activation marker CD69; after 5 days, the percentage of OVA(257-264)-specific CD8+ cells expressing high levels of CD44 increased. This cell subpopulation showed decreased expression of IL-7Rα, indicating that BLS-OVA(257-264) induced the generation of CD8+ effector cells. BLS-OVA(257-264) was cross presented in vitro independently of the presence of a functional TLR4 in the DCs. Finally, we show that immunization of wild type mice with the chimera BLS-OVA(257-264) without adjuvants induced a strong OVA(257-264)-specific effector cytotoxic response. This cytotoxicity is dependent on TLR4 as is not induced in mice lacking a functional receptor. These data show that TLR4 signaling is necessary for the induction of a cytotoxic response but not for antigen cross presentation.