Biology subjects

Legendre, A.

Publications and source records attributed to Legendre, A..

5 recordsLinked to original sources

bioRxiv2026

Genomic and eco-geographic features of locally adapted inversions in wild sunflowers

Chromosomal inversions are increasingly recognized as important drivers of local adaptation and ecological divergence because they suppress recombination and maintain adaptive allele combinations despite ongoing gene flow. However, the eco-evolutionary conditions favouring the establishment of such indirectly adaptive inversions, as well as the genomic features that distinguish them from other inversions remain incompletely understood. In this study, we investigated these questions in a wild sunflower system comprising two species: Helianthus debilis and Helianthus praecox, which exhibit diverse ecotypes and varying degrees of geographic overlap across Texas and Florida in the USA. To resolve the evolutionary relationships between and within these species, and identify potentially adaptive inversions, we generated haplotype-resolved reference assemblies and integrated comparative and population genomic analyses. We identified three major genetic clusters that only partially corresponded to taxonomic classifications. We further detected 156 inversions across the genome, 11 of which showed signatures consistent with a role in local adaptation. Notably, nine of the 11 putatively adaptive inversions were found in sympatric Texas populations. Together with a similar enrichment of inversions in genome assemblies from sympatric versus allopatric populations, our results suggest that inversions are more likely to evolve in heterogeneous environments with ongoing gene flow than in allopatry. Lastly, locally adaptive inversions were generally larger, contained more genes, and showed greater sequence divergence between haplotypes than other types of inversions. Our findings provide empirical support for the role of gene flow in promoting inversion establishment and identify genomic characteristics associated with indirectly adaptive inversions.

evolutionary biology↗

bioRxiv2026

A plant single nucleotide polymorphism impacts nectar sugar composition, microbial diversity and pollinator visits

Nectar is a hub for plant-pollinator interactions, yet gene-level causal links between plant genetic variation, pollinator foraging and nectar microbial assembly remain poorly resolved. Using near-isogenic lines, innovative field time-lapse monitoring of pollinator visits and long-read amplicon sequencing of nectar microbiota, we show that a natural single-nucleotide variant at a cell-wall invertase gene (HaCWINV2) controls sunflower nectar chemistry and influences both pollinators and microbes. Plants homozygous for a loss-of-function HaCWINV2 allele produce sucrose-rich nectar, resulting in fewer bee visits under field conditions, while bumblebee visitation remained unaffected. In pollinator-excluded flowers, invertase-deficient plants harboured greater fungal diversity and compositionally distinct communities, indicating that nectar sugar profiles act as ecological filters shaping the nectar microbiome. This loss-of-function allele was found rarely and only at the heterozygote state in wild sunflowers and was fixed in 35% of cultivated lines indicating a positive selection during domestication. Our findings establish a causal link between a single gene and nectar chemistry with cascading ecological effects in a plant-pollinator system, illustrating how subtle genetic changes scale up to alter nectar traits, microbial assembly and pollinator foraging behaviour.

genetics↗

bioRxiv2026

Fine mapping and genomic analyses reveal a tandem kinase-pseudokinase candidate underlying OrDeb2-mediated resistance to Orobanche cumana in sunflower

Sunflower broomrape (Orobanche cumana Wallr.) is a holoparasitic weed that parasitizes sunflower (Helianthus annuus L.) and severely constrains yield. The OrDeb2 gene confers resistance to broomrape race G in the sunflower line DEB2. It has been previously located within a 1.38-Mbp physical region in the H. annuus XRQ reference genome that contains a cluster of receptor-like proteins and receptor-like kinases (RLKs). In this study, an OrDeb2 candidate has been proposed though high-resolution genetic and physical mapping, multi-allelic comparisons across resistant and susceptible lines, and exclusion of other potential candidates based on their function and genetic features. OrDeb2 was delimited to a 219.4-kbp region in the DEB2 genome assembly that contained six annotated protein-coding genes belonging to two groups: three small heat shock proteins (HSP20) and three RLKs. Given that the only sunflower broomrape resistance gene cloned to date encodes an RLK, the key role of RLKs in resistance to biotic stresses in plants, and the similar genetic features between RLK-type resistance genes and OrDeb2 as major dominant genes in gene-for-gene interactions, RLKs in the interval emerged as the most plausible candidates. Within them, the RLK-2 gene encoding a root-expressed full-length kinase-pseudokinase protein belonging to the tandem kinase proteins (TKPs) family was prioritized, because the other two RLKs corresponded to a truncated TKP with a stop codon within the kinase domain. RLK-2 also carried sequence variants unique to DEB2 relative to multiple susceptible genotypes. The results of this research reveal the potential role of TKP genes as new players in resistance to parasitic plants and provide a framework to dissect the genetic dialog between O. cumana and sunflower in gene-for-gene interactions.

plant biology↗

bioRxiv2023

The penetration of sunflower root tissues by the parasitic plant Orobanche cumana Wallr. is intracellular

O_LIParasitic plants cause yield losses for important crops. Among these, Orobanche cumana Wallr, sunflower broomrape, is one of the major pests for sunflower. Previous studies stated that in most cases, the haustorium, a specific parasitic plant organ, penetrates host roots intercellularly. However, host cellular mechanisms involved during the parasitic cells penetration remained poorly described. C_LIO_LIWe investigated sunflower root cellular behavior during haustorium penetration using various microscopy approaches including live cell imaging of inoculated transgenic fluorescent sunflower roots. C_LIO_LIWe showed that the haustorium of O. cumana penetrated living sunflower root tissues, as a result of the degradation of the host cell wall and the formation of a new host trans-cellular apoplastic compartment for haustorium accommodation. Moreover, broomrape induced cell divisions in outer root tissues at very early stages of the interaction, leading to localized hypertrophy at the site of broomrape attachments. C_LIO_LIThese findings are a change of paradigm in the research field of parasitic plants. They extend host root intracellular accommodation mechanisms initially shown for symbiotic and pathogenic biotrophic fungi to parasitic plants. It paves the way for future understanding and development of resistance to parasitic plants. C_LI Key messageCombination of in vivo confocal, large field and transmission electron microscopy approaches revealed how intimate the relationship between the parasitic plant broomrape (Orobanche cumana Wallr.) and its sunflower host (Helianthus annus L.) is at very early stages of their interaction.

plant biology↗

bioRxiv2022

The genomics of linkage drag in sunflower

Crop wild relatives represent valuable sources of alleles for crop improvement, including adaptation to climate change and emerging diseases. However, introgressions from wild relatives might have deleterious effects on desirable traits, including yield, due to linkage drag. Here we comprehensively analyzed the genomic and phenotypic impacts of wild introgressions into cultivated sunflower to estimate the impacts of linkage drag. First, we generated new reference sequences for seven cultivated and one wild sunflower genotype, as well as improved assemblies for two additional cultivars. Next, relying on previously generated sequences from wild donor species, we identified introgressions in the cultivated reference sequences, as well as the sequence and structural variants they contain. We then used a ridge regression model to test the effects of the introgressions on phenotypic traits in the cultivated sunflower association mapping population. We found that introgression has introduced substantial sequence and structural variation into the cultivated sunflower gene pool, including > 3,000 new genes. While introgressions reduced genetic load at protein-coding sequences and positively affected traits associated with abiotic stress resistance, they mostly had negative impacts on yield and quality traits. Introgressions found at high frequency in the cultivated gene pool had larger effects than low frequency introgressions, suggesting that the former likely were targeted by artificial selection. Also, introgressions from more distantly related species were more likely to be maladaptive than those from the wild progenitor of cultivated sunflower. Thus, pre-breeding efforts should focus, as far as possible, on closely related and fully compatible wild relatives.

genomics↗