E-Locus - Institutional Repository of the University of Crete

Home Search

Results - Details

Search command : Author="Τσαγρή" And Author="Ευθυμία"

Current Record: 17 of 30

[Add to Basket]

Identifier

000390211

Title

Δράση παραγόντων παθογένειας βακτηρίων στο μηχανισμό της γονιδιακής σίγησης

Alternative Title

Interplay of phytobacterial TTSS effectors with post transcriptional gene silencing

Author

Καραντεμίρης, Κωνσταντίνος

Thesis advisor

Πανόπουλος, Νικόλαος

Reviewer

Κοκκινίδης, Μιχαήλ
Τσαγρή Ευθυμία
Αλεξανδράκη, Δέσποινα
Γεωργακόπουλος, Δημήτριος
Βερβερίδης, Φίλιππος
Σκανδάλης, Νικόλαος

Abstract

Many plant pathogenic bacteria inject compositionally and functionally diverse repertoires of effector proteins into the plant cell interior through Type Three Secretion Systems (T3SSs)]. Plant Resistance (R) genes mediate recognition of effectors and induce Effector-Triggered Immunity. R gene mediated resistance is often expressed as localized programmed cell death (Hypersensitive Response, HR) accompanied by accumulation of antimicrobial metabolites, restricting the proliferation of biotrophic pathogens. Effector proteins promote bacterial virulence by manipulating specific physiological processes or signaling pathways to subvert host immunity and suppress plant defenses (Pattern-Triggered Immunity [PTI] and Effector-Triggered Immunity [ETI]). RNA interference (RNAi) is an immunity mechanism in which double-stranded RNAs are processed into 21-25 nt short interfering RNAs (siRNAs). RNA interference is a conserved regulatory process that has evolved as a defense mechanism in plants and animals. Plant pathogenic bacteria encounter host defenses mediated by a variety of small RNAs (miRNAs, nat-siRNAs, lsiRNAs etc). Here, we show that RNA interference is a novel negative regulator of necrosis induced by various elicitors of HR: a) Harpin (HrpZ), a protein elicitor supplied to the plant in purified form at relatively high concentrations, b) effector proteins injected through T3SS into the host cell cytosol, c) effectors produced endogenously in the plant cells following agrodelivery of effector-coding genes. At least in some cases, regulation of plant cell death by RNA interference is temperature-dependent. Plant pathogenic viruses, bacteria fungi and οomycetes encode suppressor proteins of RNA interference. Our results provide further evidence that bacterial T3S-secreted effector proteins may manipulate the plant siRNA pathways not only by suppressing but also by enhancing silencing efficiency. We provide evidence that transient expression of different members of an effector superfamily (HopF) from phytopathogenic Pseudomonas syringae in transgenic Nicotiana benthamiana line 16c over-expressing a green fluorescent protein (GFP), suppressed sense-post-transcriptional gene silencing (s-PGTS) triggered by agro infiltration of a GFP-over expressing cassette while other members of the same superfamily enhanced gene silencing. Using truncated versions of these effector proteins, we identified distinct N- and C-terminal domains that are sufficient for both silencing suppression and inhibition of plant cell death. Through targeted mutagenesis we further identified clustered residues in conserved motifs of some effector proteins that are required for silencing suppression in N. benthamiana and cell death inhibition in both N. benthamiana and Nicotiana tabacum. Finally, we provide evidence that the E3 ubiquitin ligase domain of HopAB2 as sufficient for both silencing enhancement and inhibition of plant cell death. Site-directed substitutions in the full-length HopAB2 protein which mildly reduce its E3-ligase activity also contribute in HopAB2 silencing enhancement phenotype. Our analysis extends the range of known suppressor (and enhancer) proteins from P. syringae and provides clues about the role of silencing suppression (and enhancement) in plant-microbe interactions. Furthermore, it uncovers criticalparameters for cell death inhibition by members of effector protein superfamilies. The interplay between gene silencing, plant cell death and effector proteins is discussed.

Language

Greek

Subject

Cell death

Hypersensitive response

Pseudomonas syringae

RNA silencing

RNA σίγηση

Type III secretion system

Αντίδραση υπερευαισθησίας

Κυτταρικός Θάνατος

Πρωτεΐνες-τελεστές