Alteration of cell wall xylan acetylation triggers defense responses that counterbalance the immune deficiencies of plants impaired in the β‐subunit of the heterotrimeric G‐protein

[EN] Arabidopsis heterotrimeric G-protein complex modulates pathogen-associated molecular pattern-triggeredimmunity (PTI) and disease resistance responses to different types of pathogens. It also plays a role in plantcell wall integrity as mutants impaired in the Gb-(agb1-2)orGc-subunits have an altered wall compositioncompared with wild-type plants. Here we performed a mutant screen to identify suppressors ofagb1-2(sgb) that restore susceptibility to pathogens to wild-type levels. Out of the foursgbmutants (sgb10–sgb13)identified,sgb11is a new mutant allele ofESKIMO1(ESK1), which encodes a plant-specific polysaccharideO-acetyltransferase involved in xylan acetylation. Null alleles (sgb11/esk1-7)ofESK1restore to wild-typelevels the enhanced susceptibility ofagb1-2to the necrotrophic fungusPlectosphaerella cucumerina BMM(PcBMM), but not to the bacteriumPseudomonas syringaepv.tomatoDC3000 or to the oomyceteHyaloper-onospora arabidopsidis. The enhanced resistance toPcBMMof theagb1-2 esk1-7double mutant was notthe result of the re-activation of deficient PTI responses inagb1-2. Alteration of cell wall xylan acetylationcaused byESK1impairment was accompanied by an enhanced accumulation of abscisic acid, the constitu-tive expression of genes encoding antibiotic peptides and enzymes involved in the biosynthesis of trypto-phan-derived metabolites, and the accumulation of disease resistance-related secondary metabolites anddifferent osmolites. Theseesk1-mediated responses counterbalance the defective PTI andPcBMMsuscepti-bility ofagb1-2plants, and explain the enhanced drought resistance ofesk1plants. These results suggestthat a deficient PTI-mediated resistance is partially compensated by the activation of specific cell-wall-trig-gered immune responses.SISpanish Ministry of Economy and Competitiveness (MINECO) grants BIO2012-32910 to A.M.The Australian Research Council Centre of Excellence in Plant Cell Walls and matching funding from KTH (grants to V.B) and NIGMS (R01GM065989) and NSF (MCB-1713880) to A.M.J. The Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the US Department of Energy through the grant DE-FG02-05er15671 to A.M.J. funded technical support in this study. H.M. was supported by an IEF grant (SignWALLINg-624721) from the European Union, E.M. by a Juan de la Cierva Postdoctoral Fellow from MINECO, S.S. by the BRAVE Erasmus Mundi Program (European Union), and A.M.-B. was the recipient of a PIF fellow from Universidad Politécnica de Madrid

Alteration of cell wall xylan acetylation triggers defense responses that counterbalance the immune deficiencies of plants impaired in the β-subunit of the heterotrimeric G-protein

Arabidopsis heterotrimeric G-protein complex modulates pathogen-associated molecular pattern-triggered immunity (PTI) and disease resistance responses to different types of pathogens. It also plays a role in plant cell wall integrity as mutants impaired in the Gβ- (agb1-2) or Gγ-subunits have an altered wall composition compared with wild-type plants. Here we performed a mutant screen to identify suppressors of agb1-2 (sgb) that restore susceptibility to pathogens to wild-type levels. Out of the four sgb mutants (sgb10-sgb13) identified, sgb11 is a new mutant allele of ESKIMO1 (ESK1), which encodes a plant-specific polysaccharide O-acetyltransferase involved in xylan acetylation. Null alleles (sgb11/esk1-7) of ESK1 restore to wild-type levels the enhanced susceptibility of agb1-2 to the necrotrophic fungus Plectosphaerella cucumerina BMM (PcBMM), but not to the bacterium Pseudomonas syringae pv. tomato DC3000 or to the oomycete Hyaloperonospora arabidopsidis. The enhanced resistance to PcBMM of the agb1-2 esk1-7 double mutant was not the result of the re-activation of deficient PTI responses in agb1-2. Alteration of cell wall xylan acetylation caused by ESK1 impairment was accompanied by an enhanced accumulation of abscisic acid, the constitutive expression of genes encoding antibiotic peptides and enzymes involved in the biosynthesis of tryptophan-derived metabolites, and the accumulation of disease resistance-related secondary metabolites and different osmolites. These esk1-mediated responses counterbalance the defective PTI and PcBMM susceptibility of agb1-2 plants, and explain the enhanced drought resistance of esk1 plants. These results suggest that a deficient PTI-mediated resistance is partially compensated by the activation of specific cell-wall-triggered immune responses.Viviana Escudero, Lucía Jordá, Sara Sopeña-Torres, Hugo Mélida, Eva Miedes, Antonio Muñoz-Barrios, Sanjay Swami, Danny Alexander, Lauren S. McKee, Andrea Sánchez-Vallet, Vincent Bulone, Alan M. Jones, and Antonio Molin

"Invisible burials" and fragmentation practices in Iron Age Europe:Excavations at the Monte Bernorio Necropolis (Northern Spain)

The scarcity of burial remains in large parts of Iron Age Europe, particularly in the Atlantic regions, has often led scholars to discuss the apparent “invisibility” of graves. This paper presents the results from several excavation campaigns at Monte Bernorio, one of the most important sites of the 1st millennium b.c. on the Iberian Peninsula. The fieldwork and post-excavation work carried out in the area of the necropolis have identified numerous burial pits, with complex ritual activities characterized by fragmentation and the practice of the pars pro toto. In addition, evidence for later rituals in some of the graves can be linked to ancestor worship. The results provide important insights into funerary practices in Late Iron Age Europe, leading us to rethink the very meaning of cemeteries in the study area and beyond.- Burial Traditions in Iron Age Europe - The Monte Bernorio Archaeological Zone - The 2007–2008 Necropolis Excavations - The 2015–2016 Necropolis Excavations - Post-Excavation Work and Interpretation: The Faunal and Human Remains - Structure and Chronology of Monte Bernorio Area 7 - Destruction of the Body, Commemoration in the Absence of a Corpse, and Visibility of the Mortuary Rite