Little is known about the function of host factors involved in disease susceptibility. The barley (Hordeum vulgare) ROP (RHO of plants) G-protein RACB is required for full susceptibility of the leaf epidermis to invasion by the biotrophic fungus Blumeria graminis f. sp hordei. Stable transgenic knockdown of RACB reduced the ability of barley to accommodate haustoria of B. graminis in intact epidermal leaf cells and to form hairs on the root epidermis, suggesting that RACB is a common element of root hair outgrowth and ingrowth of haustoria in leaf epidermal cells. We further identified a barley MICROTUBULE-ASSOCIATED ROP-GTPASE ACTIVATING PROTEIN (MAGAP1) interacting with RACB in yeast and in planta. Fluorescent MAGAP1 decorated cortical microtubules and was recruited by activated RACB to the cell periphery. Under fungal attack, MAGAP1-labeled microtubules built a polarized network at sites of successful defense. By contrast, microtubules loosened where the fungus succeeded in penetration. Genetic evidence suggests a function of MAGAP1 in limiting susceptibility to penetration by B. graminis. Additionally, MAGAP1 influenced the polar organization of cortical microtubules. These results add to our understanding of how intact plant cells accommodate fungal infection structures and suggest that RACB and MAGAP1 might be antagonistic players in cytoskeleton organization for fungal entry.
Certain plant receptor-like cytoplasmic kinases were reported to interact with small monomeric G-proteins of the RHO of plant (ROP; also called RAC) family in planta and to be activated by this interaction in vitro. We identified a barley (Hordeum vulgare)
In Botrytis cinerea, some components of the cAMP-dependent pathway, such as alpha subunits of heterotrimeric G proteins and the adenylate cyclase BAC, have been characterized and their impact on growth, conidiation, germination, and virulence has been demonstrated. Here, we describe the functions of more components of the cAMP cascade: the catalytic subunits BcPKA1 and BcPKA2 and the regulatory subunit BcPKAR of the cAMP-dependent protein kinase (PKA). Although Deltabcpka2 mutants showed no obvious phenotypes, growth and virulence were severely affected by deletion of both bcpka1 and bcpkaR. Similar to Deltabac, lesion development of Deltabcpka1 and DeltabcpkaR was slower than in controls and soft rot of leaves never occurred. In contrast to Deltabac, Deltabcpka1 and DeltabcpkaR mutants sporulated in planta, and growth rate, conidiation, and conidial germination were not impaired, indicating PKA-independent functions of cAMP. Unexpectedly, Deltabcpka1 and DeltabcpkaR showed identical phenotypes, suggesting the total loss of PKA activity in both mutants. The deletion of bcras2 encoding the fungal-specific Ras GTPase resulted in significantly delayed germination and decreased growth rates. Both effects could be partially restored by exogenous cAMP, suggesting that BcRAS2 activates the adenylate cyclase in addition to the Galpha subunits BCG1 and BCG3, thus influencing cAMP-dependent signal transduction.
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.
Plant RHO-like ROP proteins are multifunctional switches involved in a variety of plant signaling processes, such as growth and development, cytoskeleton organization, secretion, hormone response, generation of reactive oxygen species (ROS) and susceptibility and resistance to plant pathogens. [1][2][3][4] As molecular switches, RAC/ROPs exist in a GDP-bound inactive form and a GTP-bound active form for targeting downstream effectors. The intrinsic GTPase activity of RAC/ROP proteins is low and requires specific activation by ROPGAPs (ROP GTPASE-ACTIVATING PROTEINs). ROPGAPs are typical members of the eukaryotic RHOGAP family and contain an arginine finger in their conserved catalytic GAP domain, which is supposed to reach into the GTP-binding pocket for stimulation of the GTPase activity of RAC/ROPs, resulting in hydrolysis of GTP and RAC/ROP shutdown. 5In the monocots barley or rice, several RAC/ROP proteins are involved in plant-pathogen interactions. In rice, OsRAC1 is a positive regulator of defense against the rice blast fungus Magnaporthe grisea by stimulating ROS production and cell death through interaction with an NADPH oxidase. 6,7 In barley, HvRACB was identified as susceptibility factor to penetration by Blumeria graminis f.sp hordei (Bgh), influencing actin reorganization during pathogen attack. [8][9][10][11][12] Stable knock-down of HvRACB expression inhibits penetration success of Bgh and impairs establishment and expansion of fungal haustoria in barley epidermal cells. Furthermore, HvRACB is required for initiation and elongation of barley root hairs and affects adult plant height similar the barley roP GtPase hvraCB is a susceptibility factor of barley to powdery mildew caused by the biotrophic fungus Blumeria graminis f.sp hordei (Bgh). in a recent publication, we reported about a miCrotuBuLE-aSSoCiatED roP GtPaSE-aCtiVatiNG ProtEiN (hvmaGaP1) of barley. transient-induced gene silencing or overexpression of hvmaGaP1 resulted in enhanced or reduced susceptibility to Bgh, respectively, indicating a possible hvraCB-antagonistic function of hvmaGaP1 in interaction with Bgh. hvmaGaP1 also influences the polarity of cortical microtubules in interaction with Bgh. in atroPGaP1 and atroPGaP4, arabidopsis homologs of hvmaGaP1, knockout t-DNa insertions enhanced susceptibility of arabidopsis to the virulent powdery mildew fungus Erysiphe cruciferarum, indicating functions of roPGaPs in pathogen interaction of monocots and dicots. here we discuss the role of atroPGaP1 and atroPGaP4 in arabidopsis pathogenesis of powdery mildew in some more detail.
Reference: Reiner T, Hoefle C, The Arabidopsis ROP-activated receptor-like cytoplasmic kinase RLCK VI_A3 is involved in control of basal resistance to powdery mildew and trichome branching. Plant Cell Rep 34:457-468. 2The final publication is available at Springer via http://dx.doi.org/doi: 10.1007/s00299-014-1725-1 KEY MESSAGEThe Arabidopsis receptor-like cytoplasmic kinase AtRLCK VI_A3 is activated by AtROPs and is involved in trichome branching and pathogen interaction. Key words:Receptor-like cytoplasmic kinase (RLCK), RAC/ROP GTPase, Arabidopsis thaliana, Erysiphe cruciferarum, Trichome Reference: Reiner T, Hoefle C, The Arabidopsis ROP-activated receptor-like cytoplasmic kinase RLCK VI_A3 is involved in control of basal resistance to powdery mildew and trichome branching. Plant Cell Rep 34:457-468. 3The final publication is available at Springer via http://dx.doi.org
Endlich! Ein altersgerechtes Selbststrukturierungstraining f?r Jugendliche mit ADS/ADHS, das nicht nur Konzentration und Aufmerksamkeit f?rdert, sondern auch die Lebenswelt der Teenager ber?cksichtigt. Mit einfachen Tricks gehen sie in der Gruppe ihre sozialen Kompetenzen, die Schule und das Lernen an.
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