Evolutionary tinkering of the expression of PDF1s suggests their joint effect on zinc tolerance and the response to pathogen attack

Multigenic families of Plant Defensin type 1 (PDF1) have been described in several species, including the model plant Arabidopsis thaliana as well as zinc tolerant and hyperaccumulator A. halleri. In A. thaliana, PDF1 transcripts (AtPDF1) accumulate in response to pathogen attack following synergic activation of ethylene/jasmonate pathways. However, in A. halleri, PDF1 transcripts (AhPDF1) are constitutively highly accumulated. Through an evolutionary approach, we investigated the possibility of A. halleri or A. thaliana species specialization in different PDF1s in conveying zinc tolerance and/or the response to pathogen attack via activation of the jasmonate (JA) signaling pathway. The accumulation of each PDF1 from both A. halleri and A. thaliana was thus compared in response to zinc excess and MeJA application. In both species, PDF1 paralogues were barely or not at all responsive to zinc. However, regarding the PDF1 response to JA signaling activation, A. thaliana had a higher number of PDF1s responding to JA signaling activation. Remarkably, in A. thaliana, a slight but significant increase in zinc tolerance was correlated with activation of the JA signaling pathway. In addition, A. halleri was found to be more tolerant to the necrotrophic pathogen Botrytis cinerea than A. thaliana. Since PDF1s are known to be promiscuous antifungal proteins able to convey zinc tolerance, we propose, on the basis of the findings of this study, that high constitutive PDF1 transcript accumulation in A. halleri is a potential way to skip the JA signaling activation step required to increase the PDF1 transcript level in the A. thaliana model species. This could ultimately represent an adaptive evolutionary process that would promote a PDF1 joint effect on both zinc tolerance and the response to pathogens in the A. halleri extremophile species

The antifungal plant defensin AhPDF1.1b is a beneficial factor involved in adaptive response to zinc overload when it is expressed in yeast cells

Antimicrobial peptides represent an expanding family of peptides involved in innate immunity of many living organisms. They show an amazing diversity in their sequence, structure, and mechanism of action. Among them, plant defensins are renowned for their antifungal activity but various side activities have also been described. Usually, a new biological role is reported along with the discovery of a new defensin and it is thus not clear if this multifunctionality exists at the family level or at the peptide level. We previously showed that the plant defensin AhPDF1.1b exhibits an unexpected role by conferring zinc tolerance to yeast and plant cells. In this paper, we further explored this activity using different yeast genetic backgrounds: especially the zrc1 mutant and an UPRE-GFP reporter yeast strain. We showed that AhPDF1.1b interferes with adaptive cell response in the endoplasmic reticulum to confer cellular zinc tolerance. We thus highlighted that, depending on its cellular localization, AhPDF1.1b exerts quite separate activities: when it is applied exogenously, it is a toxin against fungal and also root cells, but when it is expressed in yeast cells, it is a peptide that modulates the cellular adaptive response to zinc overload

The Five AhMTP1 Zinc Transporters Undergo Different Evolutionary Fates towards Adaptive Evolution to Zinc Tolerance in Arabidopsis halleri

Gene duplication is a major mechanism facilitating adaptation to changing environments. From recent genomic analyses, the acquisition of zinc hypertolerance and hyperaccumulation characters discriminating Arabidopsis halleri from its zinc sensitive/non-accumulator closest relatives Arabidopsis lyrata and Arabidopsis thaliana was proposed to rely on duplication of genes controlling zinc transport or zinc tolerance. Metal Tolerance Protein 1 (MTP1) is one of these genes. It encodes a Zn2+/H+ antiporter involved in cytoplasmic zinc detoxification and thus in zinc tolerance. MTP1 was proposed to be triplicated in A. halleri, while it is present in single copy in A. thaliana and A. lyrata. Two of the three AhMTP1 paralogues were shown to co-segregate with zinc tolerance in a BC1 progeny from a cross between A. halleri and A. lyrata. In this work, the MTP1 family was characterized at both the genomic and functional levels in A. halleri. Five MTP1 paralogues were found to be present in A. halleri, AhMTP1-A1, -A2, -B, -C, and -D. Interestingly, one of the two newly identified AhMTP1 paralogues was not fixed at least in one A. halleri population. All MTP1s were expressed, but transcript accumulation of the paralogues co-segregating with zinc tolerance in the A. halleri X A. lyrata BC1 progeny was markedly higher than that of the other paralogues. All MTP1s displayed the ability to functionally complement a Saccharomyces cerevisiæ zinc hypersensitive mutant. However, the paralogue showing the least complementation of the yeast mutant phenotype was one of the paralogues co-segregating with zinc tolerance. From our results, the hypothesis that pentaplication of MTP1 could be a major basis of the zinc tolerance character in A. halleri is strongly counter-balanced by the fact that members of the MTP1 family are likely to experience different evolutionary fates, some of which not concurring to increase zinc tolerance

A DNA education

La biologie moléculaire est l'ensemble des techniques et des découvertes qui ont permis l'analyse des processus les plus intimes du vivant, de ceux qui en assurent la pérennité et la reproduction. Elle permet de percevoir le vivant comme un réservoir et un transmetteur d'information. Au cours de ma formation universitaire, j'ai été enthousiasmée par cette discipline et j'ai conduit ma recherche autour de cette marque, autour des informations de structure, de fonction, de régulation portées par la molécule d'ADN et des conséquences phénotypiques de leur expression. Par intérêt personnel, j'ai construit mon parcours de recherche dans le domaine de la biologie végétale et c'est l'étude de la réponse des plantes aux contraintes abiotiques de l'environnement qui a constitué l'essentiel de mon activité. J'ai répondu à ma problématique en utilisant une démarche de génétique moléculaire sur la plante modèle Arabidopsis thaliana. Par mes travaux, j'ai apporté des connaissances sur la signalétique de la perception des plantes à la contrainte hydrique et sur la caractérisation des acteurs impliqués dans la réponse de la plante aux contraintes metalliques. Mes derniers travaux, m'ont amené à positionner ma problématique dans le cadre de la redondance fonctionnelle entre les différents membres de familles multigéniques et de ses conséquences en terme de destinée évolutive des différents paralogues. Le projet de recherche que je propose se situe dans la continuité de ma démarche. Il a pour but de comprendre les mécanismes d'adaptation de la plante Arabidopsis halleri aux contraintes de la teneur élevée du sol en métaux en comparaison avec la plante modèle A. thaliana, phylogénétiquement proche, mais non tolérante. Le point d'entrée moléculaire est l'étude de la famille multigénique des gènes Plant Defensin de type 1 (PDF1s). L'objectif de ce projet est d'identifier les cibles moléculaires responsables de l'importance fonctionnelle in planta des différents paralogues PDF1s pour le caractère de tolérance au zinc. La réalisation de ce projet pose les bases de l'identification des processus évolutifs qui ont permis "de recruter" pour leur fonction dans la tolérance au zinc des protéines impliquées de façon ancestrale pour leur rôle dans les processus innées de défense contre les agents pathogènes

Functional expression of Defensins for plant zinc tolerance

absen

Zinc tolerance within the Plant Defensin Family

absen

[Determination of the terminal sequences of the transposon Tn7].

International audienc

[Determination of the terminal sequences of the transposon Tn7].

International audienc

Chimeric MTP1 Gene: a Good Candidate for Zinc Biofortification of Cereals ?

International audienc