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To characterize the response of sunflower to the low levels of Cd exposure encountered in agricultural soils. Plants were exposed in hydroponics to low concentrations of Cd (2.5 nM or 20 nM) and sampled at four vegetative stages (6, 9, 14 and 19 expanded leaves). Plant growth, root Cd absorbing properties and Cd partitioning between organs were monitored along with Cd content in the xylem sap. Sunflower growth was not limited when exposed to 20 nM Cd. The amount of Cd taken up by the plant roots as well as the rate of Cd loading in xylem sap increased in direct proportion to the concentration of Cd super(2+) in the nutrient solution, suggesting that neither the root Cd absorbing capacities nor the root-to-shoot translocation of Cd were impacted by the level of Cd exposure. The partitioning of Cd between stem and leaves followed that of dry matter, regardless of the Cd treatment. The root-to-shoot partitioning of Cd at early growth stages differed from that prevailing later on. In an agricultural context, the partitioning of Cd between sunflower organs does not appear to be affected by the level of Cd exposure during vegetative growth.

Sunflower is classified as a moderately drought tolerant crop. Genotypic variations and water availability are factors that influence the root development of the crop, which is important for water absorption in deep regions of the soil. Therefore, tests in controlled water deficit environments allow evaluating a set of morphoanatomical characteristics of the root system that attribute tolerance to water deficit, contributing to sunflower genetic improvement programs. The objective of this study was to identify a set of root morphoanatomical characteristics of four sunflower genotypes subjected to controlled water deficit. We tested four commercial sunflower genotypes (OLISUN03, AGUARÁ06, HELIO250 and BRS323) under well-irrigated (field capacity) and water restriction (40% of field capacity) conditions, completely randomized design with six replicates was applied, grown in rhizotron pot, allowing to evaluate root development through imaging and anatomical characteristics related to water absorption in different regions of the sunflower root system. Plants under water deficit showed changes that contributed to water absorption in different positions of root development. Under water deficit, the tissue differentiation occurred first near the root apex, while at field capacity differentiation occurred close to the root base. In the condition of water deficit, it was verified narrow root system architecture (RSA) for the genotype OLISUN03, deep RSA for BRS323, reduced endoderm thickness in OLISUN03 and vascular cylinder area in AGUARÁ06. In general, water deficit promoted changes in the morphological and anatomical characteristics of the root system. Morphological and anatomical modifications of the root system contribute to the anchoring and absorption of water and nutrients in places with little water availability in the soil.

The domesticated sunflower, Helianthus annuus L., is a global oil crop that has promise for climate change adaptation, because it can maintain stable yields across a wide variety of environmental conditions, including drought. Even greater resilience is achievable through the mining of resistance alleles from compatible wild sunflower relatives, including numerous extremophile species. Here we report a high-quality reference for the sunflower genome (3.6 gigabases), together with extensive transcriptomic data from vegetative and floral organs. The genome mostly consists of highly similar, related sequences and required single-molecule real-time sequencing technologies for successful assembly. Genome analyses enabled the reconstruction of the evolutionary history of the Asterids, further establishing the existence of a whole-genome triplication at the base of the Asterids II clade and a sunflower-specific whole-genome duplication around 29 million years ago. An integrative approach combining quantitative genetics, expression and diversity data permitted development of comprehensive gene networks for two major breeding traits, flowering time and oil metabolism, and revealed new candidate genes in these networks. We found that the genomic architecture of flowering time has been shaped by the most recent whole-genome duplication, which suggests that ancient paralogues can remain in the same regulatory networks for dozens of millions of years. This genome represents a cornerstone for future research programs aiming to exploit genetic diversity to improve biotic and abiotic stress resistance and oil production, while also considering agricultural constraints and human nutritional needs.

Root and rhizosphere microbial communities can affect plant health, but it remains undetermined how plant domestication may influence these bacterial and fungal communities. We grew 33 sunflower (Helianthus annuus) strains (n = 5) that varied in their extent of domestication and assessed rhizosphere and root endosphere bacterial and fungal communities. We also assessed fungal communities in the sunflower seeds to investigate the degree to which root and rhizosphere communities were influenced by vertical transmission of the microbiome through seeds. Neither root nor rhizosphere bacterial communities were affected by the extent of sunflower domestication, but domestication did affect the composition of rhizosphere fungal communities. In particular, more modern sunflower strains had lower relative abundances of putative fungal pathogens. Seed-associated fungal communities strongly differed across strains, but several lines of evidence suggest that there is minimal vertical transmission of fungi from seeds to the adult plants. Our results indicate that plant-associated fungal communities are more strongly influenced by host genetic factors and plant breeding than bacterial communities, a finding that could influence strategies for optimizing microbial communities to improve crop yields.

Background Salinity is one major abiotic stress affecting photosynthesis, plant growth, and development, resulting in low-input crops. Although photosynthesis underlies the substantial productivity and biomass storage of crop yield, the response of the sunflower photosynthetic machinery to salinity imposition and how H 2 S mitigates the salinity-induced photosynthetic injury remains largely unclear. Seed priming with 0.5 mM NaHS, as a donor of H 2 S, was adopted to analyze this issue under NaCl stress. Primed and nonprime seeds were established in nonsaline soil irrigated with tape water for 14 d, and then the seedlings were exposed to 150 mM NaCl for 7 d under controlled growth conditions. Results Salinity stress significantly harmed plant growth, photosynthetic parameters, the structural integrity of chloroplasts, and mesophyll cells. H 2 S priming improved the growth parameters, relative water content, stomatal density and aperture, photosynthetic pigments, photochemical efficiency of PSII, photosynthetic performance, soluble sugar as well as soluble protein contents while reducing proline and ABA under salinity. H 2 S also boosted the transcriptional level of ribulose 1,5-bisphosphate carboxylase small subunit gene ( HaRBCS ). Further, the transmission electron microscope showed that under H 2 S priming and salinity stress, mesophyll cells maintained their cell membrane integrity and integrated chloroplasts with well-developed thylakoid membranes. Conclusion The results underscore the importance of H 2 S priming in maintaining photochemical efficiency, Rubisco activity, and preserving the chloroplast structure which participates in salinity stress adaptation, and possibly sunflower productivity under salinity imposition. This underpins retaining and minimizing the injury to the photosynthetic machinery to be a crucial trait in response of sunflower to salinity stress.

The development of modern crops typically involves both selection and hybridization, but to date most studies have focused on the former. In the present study, we explore how both processes, and their interactions, have molded the genome of the cultivated sunflower (Helianthus annuus), a globally important oilseed. To identify genes targeted by selection during the domestication and improvement of sunflower, and to detect post‐domestication hybridization with wild species, we analyzed transcriptome sequences of 80 genotypes, including wild, landrace, and modern lines of H. annuus, as well as two cross‐compatible wild relatives, Helianthus argophyllus and Helianthus petiolaris. Outlier analyses identified 122 and 15 candidate genes associated with domestication and improvement, respectively. As in several previous studies, genes putatively involved in oil biosynthesis were the most extreme outliers. Additionally, several promising associations were observed with previously mapped quantitative trait loci (QTLs), such as branching. Admixture analyses revealed that all the modern cultivar genomes we examined contained one or more introgressions from wild populations, with every chromosome having evidence of introgression in at least one modern line. Cumulatively, introgressions cover c. 10% of the cultivated sunflower genome. Surprisingly, introgressions do not avoid candidate domestication genes, probably because of the reintroduction of branching.

Given the rising risk of extreme weather caused by climate change, enhancement of abiotic stress resistance in crops is increasingly urgent. But will the development of stress-resistant cultivars come at the cost of yield under ideal conditions? We hypothesize that this need not be inevitable, because resistance alleles with minimal pleiotropic costs may evade artificial selection and be retained in crop germplasm. Genome-wide association (GWA) analyses for variation in plant performance and flooding response were conducted in cultivated sunflower, a globally important oilseed. We observed broad variation in flooding responses among genotypes. Flooding resistance was not strongly correlated with performance in control conditions, suggesting no inherent trade-offs. Consistent with this finding, we identified a subset of loci conferring flooding resistance, but lacking antagonistic effects on growth. Genetic diversity loss at candidate genes underlying these loci was significantly less than for other resistance genes during cultivated sunflower evolution. Despite bottlenecks associated with domestication and improvement, low-cost resistance alleles remain within the cultivated sunflower gene pool. Thus, development of cultivars that are both flooding-tolerant and highly productive should be straightforward. Results further indicate that estimates of pleiotropic costs from GWA analyses explain, in part, patterns of diversity loss in crop genomes.

Microbial biosurfactants are valued for their surface activity and emulsifying properties; among them, rhamnolipids—primarily produced by  Pseudomonas  species—are the most prominent. Pseudomonas  sp., a plant growth-promoting rhizobacterium, is also known to enhance heavy metal (HM) uptake in Helianthus annuus L. In this study, we produced biosurfactants from Pseudomonas aeruginosa  strain ZF2MGHSO (Rha1) and Pseudomonas sp. strain AHE16 (Rha2). Gas chromatography−mass spectrometry (GC–MS) analysis confirmed that the purified biosurfactant was composed of rhamnolipids. We evaluated the effects of Rha1 and Rha2 on Cd and Zn uptake and  HaZIP1  gene expression in sunflower plants grown in contaminated soil. Both rhamnolipids significantly increased Zn and Cd accumulation in roots and shoots, with the highest root Zn (724 ± 3 mg g⁻ 1 DW) and Cd (173 ± 2 mg g⁻ 1 DW) levels recorded in Rha1-treated plants. In shoots, Zn concentrations reached 460 ± 4 mg g⁻ 1 DW with Rha1 and 426 ± 3 mg g⁻ 1 DW with Rha2, compared to 405 ± 3 mg g⁻ 1 DW in control. The relative expression of HaZIP1 was significantly upregulated in both roots and shoots under rhamnolipid treatments. In Rha1-treated plants, expression levels increased ~ 6.9-fold in roots and ~ 4.8-fold in shoots compared to control. Rha2 treatment led to ~ 6.0-fold and ~ 4.1-fold increases in roots and shoots, respectively. Our findings suggest that  HaZIP1  plays a pivotal role in the uptake and accumulation of zinc and cadmium in sunflower plants grown in contaminated soil. Overall, our study highlights the potential of biosurfactant-enhanced phytoremediation using sunflower plants as an efficient, environmentally sustainable strategy for remediating heavy metal-contaminated soils.

The major genes controlling sunflower downy mildew resistance have been designated as Pl genes. Ten of the more than 20 Pl genes reported have been mapped. In this study, we report the molecular mapping of gene Pl sub(16) in a sunflower downy mildew differential line, HA-R4. It was mapped on the lower end of linkage group (LG) 1 of the sunflower reference map, with 12 markers covering a distance of 78.9 cM. One dominant simple sequence repeat (SSR) marker, ORS1008, co-segregated with Pl sub(16), and another co-dominant expressed sequence tag (EST)-SSR marker, HT636, was located 0.3 cM proximal to the Pl sub(16) gene. The HT636 marker was also closely linked to the Pl sub(13) gene in another sunflower differential line, HA-R5. Thus the Pl sub(16) and Pl sub(13) genes were mapped to a similar position on LG 1 that is different from the previously reported Pl sub(14) gene. When the co-segregating and tightly linked markers for the Pl sub(16) gene were applied to other germplasms or hybrids, a unique band pattern for the ORS1008 marker was detected in HA-R4 and HA-R5 and their F sub(1) hybrids. This is the first report to provide two tightly linked markers for both the Pl sub(16) and Pl sub(13) genes, which will facilitate marker-assisted selection in sunflower resistance breeding, and provide a basis for the cloning of these genes.

Background With the progress of industrialization and urbanization, cadmium (Cd) pollution in farmland is increasingly severe, greatly affecting human health. Sunflowers possess high resistance to Cd stress and great potential for phytoremediation of Cd-contaminated soil. Previous studies have shown that humic acid (HA) effectively mitigates plant damage induced by Cd; however, its alleviating effects on sunflower plants under Cd stress remain largely unknown. Results We employed four different concentrations of HA (50, 100, 200, and 300 mg L −1 ) via foliar application to examine their ability to alleviate Cd stress on sunflower plants' growth, chlorophyll synthesis, and biochemical defense system. The results revealed that Cd stress not only reduced plant height, stem diameter, fresh and dry weight, and chlorophyll content in sunflower plants but also altered their chlorophyll fluorescence characteristics compared to the control group. After Cd stress, the photosynthetic structure was damaged and the number of PSII reactive centers per unit changed. Application of 200 mg L −1 HA promotes sunflower growth and increases chlorophyll content. HA significantly enhances antioxidant enzyme activities (SOD, POD, CAT, and APX) and reduces ROS content (O 2 − , H 2 O 2 and − OH). Totally, Application of 200 mg L −1 HA had the best effect than other concentrations to alleviate the Cd-induced stress in sunflower plants. Conclusions The foliar application of certain HA concentration exhibited the most effective alleviation of Cd-induced stress on sunflower plants. It can enhance the light energy utilization and antioxidant enzyme activities, while reduce ROS contents in sunflower plants. These findings provide a theoretical basis for using HA to mitigate Cd stress in sunflowers.