Contrasting Effects of Wild Arachis Dehydrin Under Abiotic and Biotic Stresses

Plant dehydrins (DNHs) belong to the LEA (Late Embryogenesis Abundant) protein family and are involved in responses to multiple abiotic stresses. DHNs are classified into five subclasses according to the organization of three conserved motifs (K-; Y-; and S-segments). In the present study, the DHN protein family was characterized by molecular phylogeny, exon/intron organization, protein structure, and tissue-specificity expression in eight Fabaceae species. We identified 20 DHN genes, encompassing three (YnSKn, SKn, and Kn) subclasses sharing similar gene organization and protein structure. Two additional low conserved DHN Φ-segments specific to the legume SKn-type of proteins were also found. The in silico expression patterns of DHN genes in four legume species (Arachis duranensis, A. ipaënsis, Glycine max, and Medicago truncatula) revealed that their tissue-specific regulation is associated with the presence or absence of the Y-segment. Indeed, DHN genes containing a Y-segment are mainly expressed in seeds, whereas those without the Y-segment are ubiquitously expressed. Further qRT-PCR analysis revealed that, amongst stress responsive dehydrins, a SKn-type DHN gene from A. duranensis (AdDHN1) showed opposite response to biotic and abiotic stress with a positive regulation under water deficit and negative regulation upon nematode infection. Furthermore, transgenic Arabidopsis lines overexpressing (OE) AdDHN1 displayed improved tolerance to multiple abiotic stresses (freezing and drought) but increased susceptibility to the biotrophic root-knot nematode (RKN) Meloidogyne incognita. This contradictory role of AdDHN1 in responses to abiotic and biotic stresses was further investigated by qRT-PCR analysis of transgenic plants using a set of stress-responsive genes involved in the abscisic acid (ABA) and jasmonic acid (JA) signaling pathways and suggested an involvement of DHN overexpression in these stress-signaling pathways

Contrasting effects of wild arachis dehydrin under abiotic and biotic stresses

Plant dehydrins (DNHs) belong to the LEA (Late Embryogenesis Abundant) protein family and are involved in responses to multiple abiotic stresses. DHNs are classified into five subclasses according to the organization of three conserved motifs (K-; Y-; and S-segments). In the present study, the DHN protein family was characterized by molecular phylogeny, exon/intron organization, protein structure, and tissue-specificity expression in eight Fabaceae species. We identified 20 DHN genes, encompassing three (YnSKn, SKn, and K-n) subclasses sharing similar gene organization and protein structure. Two additional low conserved DHN Phi-segments specific to the legume SKn-type of proteins were also found. The in silico expression patterns of DHN genes in four legume species (Arachis duranensis, A. ipaensis, Glycine max, and Medicago truncatula) revealed that their tissue-specific regulation is associated with the presence or absence of the Y-segment. Indeed, DHN genes containing a Y-segment are mainly expressed in seeds, whereas those without the Y-segment are ubiquitously expressed. Further qRT-PCR analysis revealed that, amongst stress responsive dehydrins, a SKn-type DHN gene from A. duranensis (AdDHN1) showed opposite response to biotic and abiotic stress with a positive regulation under water deficit and negative regulation upon nematode infection. Furthermore, transgenic Arabidopsis lines overexpressing (OE) AdDHN1 displayed improved tolerance to multiple abiotic stresses (freezing and drought) but increased susceptibility to the biotrophic root-knot nematode (RKN) Meloidogyne incognita. This contradictory role of AdDHN1 in responses to abiotic and biotic stresses was further investigated by qRT-PCR analysis of transgenic plants using a set of stress-responsive genes involved in the abscisic acid (ABA) and jasmonic acid (JA) signaling pathways and suggested an involvement of DHN overexpression in these stress-signaling pathways

Defining the combined stress response in wild Arachis

International audienceNematodes and drought are major constraints in tropical agriculture and often occur simultaneously. Plant responses to these stresses are complex and require crosstalk between biotic and abiotic signaling pathways. In this study, we explored the transcriptome data of wild Arachis species subjected to drought (A-metaDEG) and the root-knot nematode Meloidogyne arenaria (B-metaDEG) via meta-analysis, to identify core-stress responsive genes to each individual and concurrent stresses in these species. Transcriptome analysis of a nematode/drought bioassay (cross-stress) showed that the set of stress responsive DEGs to concurrent stress is distinct from those resulting from overlapping A- and B-metaDEGs, indicating a specialized and unique response to combined stresses in wild Arachis . Whilst individual biotic and abiotic stresses elicit hormone-responsive genes, most notably in the jasmonic and abscisic acid pathways, combined stresses seem to trigger mainly the ethylene hormone pathway. The overexpression of a cross-stress tolerance candidate gene identified here, an endochitinase-encoding gene ( AsECHI ) from Arachis stenosperma , reduced up to 30% of M. incognita infection and increased post-drought recovery in Arabidopsis plants submitted to both stresses. The elucidation of the network of cross-stress responsive genes in Arachis contributes to better understanding the complex regulation of biotic and abiotic responses in plants facilitating more adequate crop breeding for combined stress tolerance

Early responses to dehydration in contrasting wild <i>Arachis</i> species

<div><p>Wild peanut relatives (<i>Arachis</i> spp.) are genetically diverse and were selected throughout evolution to a range of environments constituting, therefore, an important source of allelic diversity for abiotic stress tolerance. In particular, <i>A</i>. <i>duranensis</i> and <i>A</i>. <i>stenosperma</i>, the parents of the reference <i>Arachis</i> A-genome genetic map, show contrasting transpiration behavior under limited water conditions. This study aimed to build a comprehensive gene expression profile of these two wild species under dehydration stress caused by the withdrawal of hydroponic nutrient solution. For this purpose, roots of both genotypes were collected at seven time-points during the early stages of dehydration and used to construct cDNA paired-end libraries. Physiological analyses indicated initial differences in gas exchange parameters between the drought-tolerant genotype of <i>A</i>. <i>duranensis</i> and the drought-sensitive genotype of <i>A</i>. <i>stenosperma</i>. High-quality Illumina reads were mapped against the <i>A</i>. <i>duranensis</i> reference genome and resulted in the identification of 1,235 and 799 Differentially Expressed Genes (DEGs) that responded to the stress treatment in roots of <i>A</i>. <i>duranensis</i> and <i>A</i>. <i>stenosperma</i>, respectively. Further analysis, including functional annotation and identification of biological pathways represented by these DEGs confirmed the distinct gene expression behavior of the two contrasting <i>Arachis</i> species genotypes under dehydration stress. Some species-exclusive and common DEGs were then selected for qRT-PCR analysis, which corroborated the <i>in silico</i> expression profiling. These included genes coding for regulators and effectors involved in drought tolerance responses, such as activation of osmosensing molecular cascades, control of hormone and osmolyte content, and protection of macromolecules. This dataset of transcripts induced during the dehydration process in two wild <i>Arachis</i> genotypes constitute new tools for the understanding of the distinct gene regulation processes in these closely related species but with contrasting drought responsiveness. In addition, our findings provide insights into the nature of drought tolerance in wild germoplasm, which might be explored as novel sources of diversity and useful wild alleles to develop climate-resilient crop varieties.</p></div

Circos plot detailing chromosome distribution of DEGs.

<p>Distribution of the 1,602 DEGs in the ten chromosomes of <i>A</i>. <i>duranensis</i> (A01 to A10). The outer lines represent exclusive <i>A</i>. <i>duranensis</i> (red) and <i>A</i>. <i>stenosperma</i> (blue) and common (green) DEGs. The inner dots represent the distribution of Log2FC values for each up- and downregulated DEG in <i>A</i>. <i>duranensis</i> (red) and <i>A</i>. <i>stenosperma</i> (blue), with the line indicating Log2FC = 0.</p

Expression of DEGs as determined by qRT-PCR.

<p>Relative quantification of mRNA levels of 15 candidate genes in <i>A</i>. <i>duranensis</i> roots during the dehydration treatment and collected after 25 (T25); 50 (T50); 75 (T75); 100 (T100); 125 (T125) and 150 (T150) min, relative to control (T0). Bars represent the standard deviation of three biological replicates. Significantly (P < 0.05) up- or downregulated genes are indicated by asterisks.</p

Clusters of Ortholog Groups (OGs) from four legume species.

<p>Venn diagram indicating the number of Ortholog Groups (OGs) among <i>Arachis duranensis; Arachis ipaënsis; Glycine max; and Phaseolus vulgaris</i>. The number of DEGs in the different groups is in parentheses.</p

Overview of DEGs expression patterns.

<p>MapMan analysis showing molecular functional categories of DEGs expression patterns in roots of dehydration-stressed plants of <i>A</i>. <i>duranensis</i> (DD) and <i>A</i>. <i>stenosperma</i> (SD) relative to control. Squares show the different genes encoding proteins related to drought perception and oxidative responses (A) and carbohydrate and amino acid metabolism steps (B). Upregulated genes are indicated by red squares and downregulated by blue squares.</p

Physiological analysis of <i>Arachis</i> spp. plants during the early stages of dehydration.

<p>A) Photosynthetic rate; B) Stomatal conductance; C) Transpiration rate; D) Leaf temperature; E) Leaf vapor pressure deficit; and F) Internal CO₂ concentration of <i>A</i>. <i>duranensis</i> and <i>A</i>. <i>stenosperma</i> plants subjected to dehydration. Data represent averages calculated over the early stages (0, 25 and 50 min) of the drought imposition and standard error. Statistically significant differences (n = 3, Student’s t-test, p<0.05) are indicated by asterisk.</p

Summary of sequencing data.

<p>Illumina HiSeq2000 sequencing data of <i>Arachis</i> spp. transcriptome and mapping of reads to the reference <i>A</i>. <i>duranensis</i> genome.</p