Biology subjects

Azzopardi, M.

Publications and source records attributed to Azzopardi, M..

3 recordsLinked to original sources

bioRxiv2024

Identification of novel genes responsible for a pollen killer present in local natural populations of Arabidopsis thaliana

Gamete killers are genetic loci that distort segregation in the progeny of hybrids because the killer allele promotes the elimination of the gametes that carry the sensitive allele. They are widely distributed in eukaryotes and are important for understanding genome evolution and speciation. We had previously identified a pollen killer in hybrids between two distant natural accessions of Arabidopsis thaliana. This pollen killer involves three genetically linked genes, and we previously reported the identification of the gene encoding the antidote that protects pollen grains from the killer activity. In this study, we identified the two other genes of the pollen killer by using CRISPR-Cas9 induced mutants. These two genes are necessary for the killer activity that we demonstrated to be specific to pollen. The cellular localization of the pollen killer encoded proteins indicates that the pollen killer activity involves the mitochondria. Sequence analyses reveal predicted domains from the same families in the killer proteins. In addition, the C-terminal half of one of the killer proteins is identical to the antidote, and one amino acid, crucial for the antidote activity, is also essential for the killer function. Investigating more than 700 worldwide accessions of A. thaliana, we confirmed that the locus is subject to important structural rearrangements and copy number variation. By exploiting available de novo genomic sequences, we propose a scenario for the emergence of this pollen killer in A. thaliana. Furthermore, we report the co-occurrence and behavior of killer and sensitive genotypes in several local populations, a prerequisite for studying gamete killer evolution in the wild. This highlights the potential of the Arabidopsis model not only for functional studies of gamete killers but also for investigating their evolutionary trajectories at complementary geographical scales. Author SummaryCertain genetic elements are qualified as selfish because they favor their transmission to the progeny during reproduction to the detriment of gametes that do not carry them. These elements are widespread in fungi as well as in plants or in animals, and they are made up of two or even three components, which are specific to each species. Therefore, they must be studied on a case-by-case basis. Moreover, understanding how they appear and propagate in local population remains a major issue in evolutionary biology. Here we have characterized, in the model plant Arabidopsis, the three genes involved in such an element, called a pollen killer. This pollen killer targets the mitochondria to cause the death of pollen grains that do not carry it. We investigated the three genes in several hundred genotypes collected worldwide, giving us a global view of their diversity at the species level. We also found that some French local populations contain both sensitive and killer plants, which constitutes an invaluable resource for studying the evolution of a pollen killer in the wild.

genetics↗

bioRxiv2023

A transcriptomic dataset for investigating the Arabidopsis Unfolded Protein Response under chronic, proteotoxic endoplasmic reticulum stress

The Unfolded Protein Response (UPR) is a retrograde, ER-to-nucleus, signalling pathway which is conserved across kingdoms. In plants, it contributes to development, reproduction, immunity and tolerance to abiotic stress. This RNA sequencing dataset was produced from 14-day-old Arabidopsis thaliana seedlings challenged by tunicamycin (Tm), an antibiotic inhibiting Asn-linked glycosylation in the endoplasmic reticulum (ER), causing an ER stress and eventually activating the UPR. Wild-type (WT) and a double mutant deficient for two main actors of the UPR (INOSITOL-REQUIRING ENZYME 1A and INOSITOL-REQUIRING ENZYME 1B) were used as genetic backgrounds in our experimental setup, allowing to distinguish among differentially-expressed genes (DEGs) which ones are dependent on or independent on IRE1s. Also, shoots and roots were harvested separately to determine organ-specific transcriptomic responses to Tm. Library and sequencing were performed using DNBseq technology by the Beijing Genomics Institute. Reads were mapped and quantified against the Arabidopsis genome. Differentially-expressed genes were identified using Rflomics upon filtering and normalization by the Trimmed Mean of M-value (TMM) method. While the genotype effect was weak under mock conditions (with a total of 182 DEGs in shoots and 195 DEGs in roots), the tunicamycin effect on each genotype was characterized by several hundred of DEGs in both shoots and roots. Among these genes, 872 and 563 genes were statistically up- and down-regulated in the shoot tissues of the double mutant when compared to those of WT, respectively. In roots of Tm-challenged seedlings, 425 and 439 genes were significantly up- and down-regulated in mutants with respect to WT. We believe that our dataset could be reused for investigating any biological questions linked to ER homeostasis and its role in plant physiology. SPECIFICATIONS TABLE O_TBL View this table: org.highwire.dtl.DTLVardef@a6de12org.highwire.dtl.DTLVardef@13d7c62org.highwire.dtl.DTLVardef@1b14109org.highwire.dtl.DTLVardef@24dbaborg.highwire.dtl.DTLVardef@1d1c1e1_HPS_FORMAT_FIGEXP M_TBL C_TBL

plant biology↗

bioRxiv2023

UPR pathway is required for Arabidopsis thaliana resistance to necrophic fungal pathogens.

The Unfolded Protein Response (UPR) is a retrograde signalling pathway which is activated when endoplasmic reticulum (ER) proteostasis is disturbed. Here, we have investigated by reverse genetics the contribution of such pathway in Arabidopsis thaliana response to two necrotrophic fungi of agricultural importance, Botrytis cinere a which is responsible for the development of grey mold disease, and Alternaria brassicicola which triggers black spot disease. We found that the branch of UPR dependent on the INOSITOL-REQUIRING ENZYME 1 (IRE1) and the transcription factor (TF) bZIP60 is required to restrict foliar necrotic symptoms induced by both fungi. Accordingly, focussing on B. cinerea, we provided evidence for the production of the active bZIP60 form during infection. This activation was accompanied by an increased expression of UPR-responsive genes coding for ER-localized chaperones and co-chaperones that belong to the ER-Quality Control (ER-QC) system. Furthermore, mutants deficient for two ER-QC components were also more susceptible to infection. By contrast, investigating the involvement of CELL DIVISION CYCLE 48 (CDC48) AAA+-ATPAses that assist ER-Associated Degradation (ERAD) pathway for disposal of luminal unfolded proteins, we showed that a series of mutants and transgenics are more resistant to grey mold disease. Seeking for molecular insights into how the ER could shape Arabidopsis immune response to B. cinerea, we quantified the expression of defence gene and cell death markers in single bzip60 and double ire1 mutants. However, none of those genes were mis-regulated in mutant genetic backgrounds, indicating that IRE1-bZIP60 branch of UPR modulates the Arabidopsis response to B. cinerea by a yet-to-be-identified mechanism. Interestingly, we identified the NAC053/NTL4 TF as a potential actor of this unknown mechanism, linking the UPR and proteasome stress regulon. Author summaryNecrotrophic fungi are one of the most economically significant plant pathogens worldwide, inflicting massive pre- and post-harvest losses on a wide range of fruit and vegetable crops. They adopt a necrotrophic lifestyle, deriving their nutrients predominantly from dead plant tissues to complete their life cycle. Botrytis cinerea is the causal agent of grey mold and no plant shows complete resistance towards this pathogen. The use of genetic models such as the plant Arabidopsis thaliana has partially enabled the understanding of the immunity mechanisms involved in the plants response to B. cinerea. Our work provides new insights into the cellular mechanisms of how plants cope with this pathogen. In this context, by means of a reverse genetic approach, we explored the role of the Unfolded Protein Response (UPR), a cell signalling pathway regulating protein homeostasis within the endoplasmic reticulum (ER) and thus protecting cells from a harmful over-accumulation of aberrant or misfolded proteins.

plant biology↗