Topology, Subcellular Localization, and Sequence Diversity of the Mlo Family in Plants

Devoto, Alessandra; Piffanelli, Pietro; Nilsson, IngMarie; Wallin, Erik; Panstruga, Ralph; Heijne, Gunnar von; Schulze‐Lefert, Paul

doi:10.1074/jbc.274.49.34993

Cited by 262 publications

(228 citation statements)

References 58 publications

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“…Receptor kinases are also directly coupled by G proteins [32]. In higher plants, the MLO gene family has been demonstrated experimentally to have a 7-transmembrane domain topology similar to GPCRs in animals, with an estimated 35 MLO genes in Arabidopsis, one might be a G protein coupled receptor [33]. It would be interesting to investigate whether the action of a GPCR could functionally link the heterotrimeric G protein with BR signal response.…”

Section: Discussionmentioning

confidence: 99%

Heterotrimeric G protein α subunit is involved in rice brassinosteroid response

Wang

et al. 2006

Cell Res

112

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Heterotrimeric G proteins are known to function as messengers in numerous signal transduction pathways. The null mutation of RGA (rice heterotrimeric G protein α subunit), which encodes the α subunit of heterotrimeric G protein in rice, causes severe dwarfism and reduced responsiveness to gibberellic acid in rice. However, less is known about heterotrimeric G protein in brassinosteroid (BR) signaling, one of the well-understood phytohormone pathways. In the present study, we used root elongation inhibition assay, lamina inclination assay and coleoptile elongation analysis to demonstrated reduced sensitivity of d1 mutant plants (caused by the null mutation of RGA) to 24-epibrassinolide (24-epiBL), which belongs to brassinosteroids and plays a wide variety of roles in plant growth and development. Moreover, RGA transcript level was decreased in 24-epiBL-treated seedlings in a dose-dependent manner. Our results show that RGA is involved in rice brassinosteroid response, which may be beneficial to elucidate the molecular mechanisms of G protein signaling and provide a novel perspective to understand BR signaling in higher plants.

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Section: Discussionmentioning

confidence: 99%

Heterotrimeric G protein α subunit is involved in rice brassinosteroid response

Wang

et al. 2006

Cell Res

112

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“…Homozygous loss-of-function alleles of MLO (mlo) confer resistance to all known Bgh isolates, leading to the cessation of growth of fungal sporelings during cell wall penetration [36]. Barley MLO encodes the prototype of a plant-specific family of seven transmembrane domain proteins, accumulates in the plasma membrane, and interacts with the Ca 2þ sensor calmodulin via a calmodulin-binding site in its carboxy-terminal cytoplasmic tail [37][38][39][40]. The ror2 mutation was originally isolated as suppressor of mlo resistance (in a mlo null mutant background) and partially restores the susceptibility of mlo mutants to Bgh [41], suggesting that MLO might directly or indirectly antagonise ROR2 function.…”

Section: Suppression Of Disease Resistance At the Cell Wallmentioning

confidence: 99%

Knocking on the heaven’s wall: pathogenesis of and resistance to biotrophic fungi at the cell wall

Schulze‐Lefert

2004

Current Opinion in Plant Biology

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124

101

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New findings challenge the traditional view of the plant cell wall as passive structural barrier to invasion by fungal microorganisms. A surveillance system for cell wall integrity appears to sense perturbation of the cell wall structure upon fungal attack and is interconnected with known plant defence signalling pathways. Biotrophic fungi might manipulate this surveillance system for the establishment of biotrophy. The attempts of fungi to invade also induce a sub-cellular polarisation in attacked cells, which activates an ancient vesicle-associated resistance response that possibly enables the focal transport of regulatory cargo and the secretion of toxic cargo. The underlying resistance machinery might have been subverted by biotrophic fungi for pathogenesis. IntroductionPenetration through the plant cell wall represents an Achilles heel in the pathogenesis of most biotrophic fungi and marks a lifestyle transition from extra-cellular to invasive growth. Modification of the plant cell wall was recognised for the first time as potential resistance mechanism almost 80 years ago following work in which 78 plant species and varieties were challenged with Alternaria spp. and other leaf-spotting fungi [1]. The termination of fungal pathogenesis at the cell wall was commonly associated with wall 'thickenings' and the formation of local additions or 'callosities' in the paramural space (i.e. the space between the cell wall and the plasma membrane). Formation of these cell wall appositions (CWAs) or papillae is usually accompanied by a co-localised accumulation of phenolics and reactive oxygen species [2][3][4][5][6]. The complex process of sub-cellular cell wall remodelling is tightly linked to the rapid disassembly and subsequent focal reassembly of the plant cytoskeleton at fungal entry sites, which is indicative of a pathogen-triggered cell polarisation [6][7][8][9]. There has been a long-standing controversy, however, over whether CWAs function in disease resistance or facilitate the entry of fungal pathogens into host cells by providing a structural collar for the intruder. New molecular genetic data from Arabidopsis and barley have indeed revealed that molecular processes at and in CWAs have Janus-faced functions, that is, functions for fungal pathogenesis and in resistance responses. Focal vesicle transport and vesicle fusion events that are dependent on SNAP (soluble N-ethylmaleimide-sensitive-factor-association protein) receptor (SNARE) proteins at the plasma membrane emerge as potential common underlying mechanisms that might be interconnected with a poorly understood cell wall integrity surveillance system. In this review, I discuss the seemingly paradoxical functions of these processes in establishing the biotrophic lifestyle and in disease resistance at the cell periphery.Linking cell wall structure to biotic stress signalling Callose, a (1!3)-b-D-glucan, has long been known to be synthesised and deposited rapidly at CWAs upon microbial attack. This polymer was thought to contribute to a physical barrie...

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“…The latter is expressed exclusively via penetration resistance, which is accompanied by accumulation of hydrogen peroxide but not by detectable O 2 À generation Schulze-Lefert and Vogel, 2000). The wild-type MLO protein is a seventransmembrane-protein reminiscent of G-protein-coupled receptors in animals and fungi (Devoto et al, 1999). It could be excluded that MLO signalling in susceptibility to Bgh depends on heterotrimeric G-proteins (Kim et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Functional analysis of barley RAC/ROP G‐protein family members in susceptibility to the powdery mildew fungus

et al. 2003

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SummarySmall monomeric G-proteins of the plant ras (rat sarcome oncogene product) related C3 botulinum toxin substrate (RAC)/Rho of plants (ROP) family are molecular switches in signal transduction of many cellular processes. RAC/ROPs regulate hormone effects, subcellular gradients of Ca 2 , the organisation of the actin cytoskeleton and the production of reactive oxygen intermediates. Therefore, we followed a genetic bottom-up strategy to study the role of these proteins during the interaction of barley (Hordeum vulgare L.) with the fungal biotrophic pathogen Blumeria graminis f.sp. hordei (Bgh). We identi®ed six barley RAC/ ROP proteins and studied their gene expression. Five out of six Rac/Rop genes were expressed constitutively in the leaf epidermis, which is the site of interaction with Bgh. None of the genes showed enhancement of mRNA abundance after inoculation with Bgh. After microprojectile mediated transformation of single barley epidermal cells with constitutively activated mutant RAC/ROP proteins, we found an RAC/ ROP-speci®c enhancement of pathogen accessibility, tagging HvRACB, HvRAC3 and HvROP6 as host proteins potentially involved in the establishment of susceptibility to Bgh. Confocal laser scanning microscopy (CLSM) of green¯uorescent protein (GFP):HvRAC/ROP-transformed cells revealed varying strengths of plasma membrane association of barley RAC/ROPs. The C-terminal CAAX motif for presumable prenylation or the C-terminal hypervariable region (HVR), respectively, were required for membrane association of the RAC/ROPs. Proper intracellular localisation was essential for HvRACB and HvRAC3 function. Together, our data support the view that different paths of host signal transduction via RAC/ROP G-proteins are involved in processes supporting parasitic entry into epidermal host cells.

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Topology, Subcellular Localization, and Sequence Diversity of the Mlo Family in Plants

Cited by 262 publications

References 58 publications

Heterotrimeric G protein α subunit is involved in rice brassinosteroid response

Heterotrimeric G protein α subunit is involved in rice brassinosteroid response

Knocking on the heaven’s wall: pathogenesis of and resistance to biotrophic fungi at the cell wall

Functional analysis of barley RAC/ROP G‐protein family members in susceptibility to the powdery mildew fungus

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