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1. Genetic basis of octanoic acid resistance in Drosophila sechellia : functional analysis of a fine‐mapped region

   https://doi.org/10.1111/mec.14001  

   Andrade López, J. M. ; Lanno, S. M. ; Auerbach, J. M. ; Moskowitz, E. C. ; Sligar, L. A. ; Wittkopp, P. J. ; Coolon, J. D. ( February 2017 , Molecular Ecology)

   Drosophila sechelliais a species of fruit fly endemic to the Seychelles islands. Unlike its generalist sister species,D. sechelliahas evolved to be a specialist on the host plantMorinda citrifolia. This specialization is interesting because the plant's fruit contains secondary defence compounds, primarily octanoic acid (OA), that are lethal to most other Drosophilids. Although ecological and behavioural adaptations to this toxic fruit are known, the genetic basis for evolutionary changes inOAresistance is not. Prior work showed that a genomic region on chromosome 3R containing 18 genes has the greatest contribution to differences inOAresistance betweenD. sechelliaandD. simulans. To determine which gene(s) in this region might be involved in the evolutionary change inOAresistance, we knocked down expression of each gene in this region inD. melanogasterwithRNAinterference (RNAi) (i) ubiquitously throughout development, (ii) during only the adult stage and (iii) within specific tissues. We identified three neighbouring genes in theOsirisfamily,Osiris 6(Osi6),Osi7andOsi8, that led to decreasedOAresistance when ubiquitously knocked down. Tissue‐specificRNAi, however, showed that decreasing expression ofOsi6andOsi7specifically in the fat body and/or salivary glands increasedOAresistance. Gene expression analyses ofOsi6andOsi7revealed that while standing levels of expression are higher inD. sechellia,Osi6expression is significantly downregulated in salivary glands in response toOAexposure, suggesting that evolved tissue‐specific environmental plasticity ofOsi6expression may be responsible forOAresistance inD. sechellia.

    

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2. Contrasting effects of Symbiodinium identity on coral host transcriptional profiles across latitudes

   https://doi.org/10.1111/mec.14774  

   Barfield, Sarah J. ; Aglyamova, Galina V. ; Bay, Line K. ; Matz, Mikhail V. ( July 2018 , Molecular Ecology)

   Reef‐building corals can increase their resistance to heat‐induced bleaching through adaptation and acclimatization and/or by associating with a more thermo‐tolerant strain of algal symbiont (Symbiodiniumsp.). Here, we show that these two adaptive pathways interact. We collectedAcropora milleporacorals from two contrasting thermal environments on the Great Barrier Reef: cooler, mid‐latitude Orpheus Island, where all corals hosted a heat‐sensitive clade CSymbiodinium, and warmer, low‐latitude Wilkie Island, where corals hosted either a clade C or a more thermo‐tolerant clade D. Corals were kept in a benign common garden to reveal differences in baseline gene expression, reflecting prior adaptation/long‐term acclimatization. Model‐based analysis identified gene expression differences between Wilkie and Orpheus corals that were negatively correlated with previously described transcriptome‐wide signatures of heat stress, signifying generally elevated thermotolerance of Wilkie corals. Yet, model‐free analyses of gene expression revealed that Wilkie corals hosting clade C were distinct from Wilkie corals hosting clade D, whereas Orpheus corals were more variable. Wilkie corals hosting clade C symbionts exhibited unique functional signatures, including downregulation of histone proteins and ion channels and upregulation of chaperones andRNAprocessing genes, putatively representing constitutive “frontloading” of stress response genes. Furthermore, clade CSymbiodiniumexhibited constitutive expression differences between Wilkie and Orpheus, indicative of contrasting life history strategies. Our results demonstrate that hosting alternativeSymbiodiniumtypes is associated with different pathways of local adaptation for the coral host. These interactions could play a significant role in setting the direction of genetic adaptation to global warming in the two symbiotic partners.

    

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3. Use of virus‐induced gene silencing to characterize genes involved in modulating hypersensitive cell death in maize

   https://doi.org/10.1111/mpp.12999  

   Murphree, Colin ; Kim, Saet‐Byul ; Karre, Shailesh ; Samira, Rozalynne ; Balint‐Kurti, Peter ( October 2020 , Molecular Plant Pathology)

   Plant disease resistance proteins (R‐proteins) detect specific pathogen‐derived molecules, triggering a defence response often including a rapid localized cell death at the point of pathogen penetration called the hypersensitive response (HR). The maizeRp1‐D21gene encodes a protein that triggers a spontaneous HR causing spots on leaves in the absence of any pathogen. Previously, we used fine mapping and functional analysis in aNicotiana benthamianatransient expression system to identify and characterize a number of genes associated with variation inRp1‐D21‐induced HR. Here we describe a system for characterizing genes mediating HR, using virus‐induced gene silencing (VIGS) in a maize line carryingRp1‐D21. We assess the roles of 12 candidate genes. Three of these genes,SGT1,RAR1, andHSP90, are required for HR induced by a number of R‐proteins across several plant–pathogen systems. We confirmed that maize HSP90 was required for fullRp1‐D21‐induced HR. However, suppression of SGT1 expression unexpectedly increased the severity ofRp1‐D21‐induced HR while suppression of RAR1 expression had no measurable effect. We confirmed the effects on HR of two genes we had previously validated in theN. benthamianasystem,hydroxycinnamoyltransferaseandcaffeoyl CoA O‐methyltransferase. We further showed the suppression the expression of two previously uncharacterized, candidate genes,IQ calmodulin binding protein(IQM3) andvacuolar protein sorting protein 37, suppressedRp1‐D21‐induced HR. This approach is an efficient way to characterize the roles of genes modulating the hypersensitive defence response and other dominant lesion phenotypes in maize.

    

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4. Sclerenchyma cell thickening through enhanced lignification induced by OsMYB30 prevents fungal penetration of rice leaves

   https://doi.org/10.1111/nph.16505  

   Li, Weitao ; Wang, Kang ; Chern, Mawsheng ; Liu, Yuchen ; Zhu, Ziwei ; Liu, Jiang ; Zhu, Xiaobo ; Yin, Junjie ; Ran, Li ; Xiong, Jun ; et al ( March 2020 , New Phytologist)

   Broad‐spectrum resistance is highly preferred in crop breeding programmes. Previously, we have reported the identification of thebroad‐spectrum resistance‐Digu 1(bsr‐d1) allele from rice Digu. Thebsr‐d1allele prevents activation ofBsr‐d1expression byMagnaporthe oryzaeinfection and degradation of H₂O₂by peroxidases, leading to resistance toM. oryzae. However, it remains unknown whether defence pathways other than H₂O₂burst and peroxidases contribute to thebsr‐d1‐mediated immunity.

   Blast resistance was determined in rice leaves by spray and punch inoculations. Target genes of OsMYB30 were identified by one‐hybrid assays in yeast and electrophoretic mobility shift assay. Lignin content was measured by phloroglucinol–HCl staining, and acetyl bromide and thioacidolysis methods.

   Here, we report the involvement of theOsMYB30gene inbsr‐d1‐mediated blast resistance. Expression ofOsMYB30was induced duringM. oryzaeinfection or whenBsr‐d1was knocked out or downregulated, as occurs inbsr‐d1plants upon infection. We further found that OsMYB30 bound to and activated the promoters of4‐coumarate:coenzyme A ligasegenes (Os4CL3andOs4CL5) resulting in accumulation of lignin subunits G and S. This action led to obvious thickening of sclerenchyma cells near the epidermis, inhibitingM. oryzaepenetration at the early stage of infection.

   Our study revealed novel components required forbsr‐d1‐mediated resistance and penetration‐dependent immunity, and advanced our understanding of broad‐spectrum disease resistance.

    

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5. JMJ14 encoded H3K4 demethylase modulates immune responses by regulating defence gene expression and pipecolic acid levels

   https://doi.org/10.1111/nph.16270  

   Li, Dan ; Liu, Ruiying ; Singh, Deepjyoti ; Yuan, Xinyu ; Kachroo, Pradeep ; Raina, Ramesh ( November 2019 , New Phytologist)

   Epigenetic modifications have emerged as an important mechanism underlying plant defence against pathogens. We examined the role of JMJ14, a Jumonji (JMJ) domain‐containing H3K4 demethylase,in local and systemic plant immune responses in Arabidopsis.

   The function of JMJ14 in local or systemic defence response was investigated by pathogen growth assays and by analysing expression and H3K4me3 enrichments of key defence genes using qPCR and ChIP‐qPCR. Salicylic acid (SA) and pipecolic acid (Pip) levels were quantified and function of JMJ14 in SA‐ and Pip‐mediated defences was analysed in Col‐0 andjmj14plants.

   jmj14mutants were compromised in both local and systemic defences. JMJ14 positively regulates pathogen‐induced H3K4me3 enrichment and expression of defence genes involved in SA‐ and Pip‐mediated defence pathways. Consequently, loss of JMJ14 results in attenuated defence gene expression and reduced Pip accumulation during establishment of systemic acquired resistance (SAR). Exogenous Pip partially restored SAR injmj14plants, suggesting that JMJ14 regulated Pip biosynthesis and other downstream factors regulate SAR injmj14plants.

   JMJ14 positively modulates defence gene expressions and Pip levels in Arabidopsis.

    

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