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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 (O2−, H2O2 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. [ABSTRACT FROM AUTHOR]

Membrane-bound fatty acid desaturase (FAD) gene family plays crucial roles in regulation of fatty acid (FA) compositions in plants. Sunflower (Helianthus annuus L.) is an important oilseed crop in the world; however, no comprehensive study on exploring the role of FAD family in relation to stress tolerance in sunflower has been performed yet. In this study, we identified 40 putative FAD genes in H. annuus (HaFAD), which were unevenly distributed across 13 of the total 17 chromosomes. Phylogenetic analysis indicated that HaFAD genes were divided into four subfamilies, as supported by highly conserved gene structures and motifs. Collinearity analysis showed that tandem duplication events played a crucial role in the expansion of HaFAD gene family. In addition, tissue-specific expression showed that 32 HaFAD genes were widely expressed in various tissues or organs of sunflower. Furthermore, qRT-PCR results revealed significant expression changes of HaFAD genes in response to abiotic (cadmium, drought) and biotic (Orobanche cumana) stresses, suggesting their important functions in response to different stresses. Therefore, our results provide insights into HaFAD gene family in response to different stresses, and some specific up-regulated genes such as HaFAD3.2 , HaADS8 , HaFAD2.1 , and HaADS9 would be the potential candidate genes for the sunflower tolerance breeding. • A total of 40 FAD genes were identified in Helianthus annuus L. • Genome-wide characterization of FAD family was conducted in sunflower. • The heatmap of 32 HaFAD s in ten different tissues and organs was established. • 33 selected HaFAD s were differentially expressed under biotic and abiotic stresses. [ABSTRACT FROM AUTHOR]

• A total of 119 WRKY genes were identified in Helianthus annuus L. • WRKYs present genetic diversity among oil crops. • Segmental and tandem duplications contribute to the expansion of sunflower WRKYs. • Expression analysis shows neo- or subfunctionalization after WRKY duplications. • Some HaWRKY genes play critical roles response to biotic and abiotic stresses. WRKY proteins constitute a large family of transcription factors that play important roles in many aspects of physiological processes and adaptation to environmental challenge. Although previous studies have identified and characterized WRKY genes from sunflower (Helianthus annuus L.) expressed sequence tag and genomic databases, the phylogenetic diversity of WRKY repertoires of oil crop species and the responses of sunflower WRKY proteins to various stressors have not been elucidated. In this study, a total of 860 WRKY members from seven oil crop species, namely, sunflower, sesame, castor bean, soybean, canola, Arachis duranensis , and Arachis ipaensis , were subjected to comparative genomic analysis. Genetic diversity within the WRKY family among these oil crop species was revealed through pairwise comparisons of orthologous groups and phylogenetic analysis. Sequence features and phylogenetic analysis revealed that the WRKY genes of oil crop species belong to well-defined groups or subgroups, and different oil plant species exhibit obvious expansion or loss to different degrees. One hundred nineteen sunflower WRKY (HaWRKY) genes were found to be unevenly distributed across each chromosome. Segmental and tandem duplications contributed to the expansion of group II and III WRKY genes in sunflower, respectively. The duplicated genes generally exhibit divergent expression patterns, which may indicate that neofunctionalization or subfunctionalization of these genes tends to occur after duplication. Moreover, expression profiles derived from transcriptomic data exhibited distinct expression patterns of HaWRKY genes in various tissues and in response to different stress treatments, including hormone treatments, salt and drought stress, infection by the fungus Verticillium dahliae , and colonization by the fungus Rhizoglomus irregulare. According to these results, WRKY genes may be involved in the strong adaptability of sunflower to various environments, thereby contributing to the importance of sunflower as a widely cultivated oil resource. This systematic analysis provides a foundation for further functional characterization of WRKY genes among oil crop species for the improvement of stress resistance. [ABSTRACT FROM AUTHOR]

• 50 Dof family genes were identified in sunflower. • Four groups and further nine subfamilies were classified for sunflower Dof genes. • Segmental duplications contribute to expansion of sunflower Dof genes. • HaDof genes may be involved in hormone response and abiotic stress resistance. DNA binding with one finger (Dof), plant-specific zinc finger transcription factors, can participate in various physiological and biochemical processes during the life of plants. As one of the most important oil crops in the world, sunflower (Helianthus annuus L.) has significant economic and ornamental value. However, a systematic analysis of H. annuus Dof (HaDof) members and their functions has not been extensively conducted. In this study, we identified 50 HaDof genes that are unevenly distributed on 17 chromosomes of sunflower. We present a comprehensive overview of the HaDof genes, including their chromosome locations, phylogenetic analysis, and expression profile characterization. Phylogenetic analysis classified the 366 Dof members identified from 11 species into four groups (further subdivided into nine subfamilies). Segmental duplications are predominantly contributed to the expansion of sunflower Dof genes, and all segmental duplicate gene pairs are under purifying selection due to strong evolutionary constraints. Furthermore, we observed differential expression patterns for HaDof genes in normal tissues as well as under hormone treatment or abiotic stress conditions by analyzing RNA-seq data from previous studies and RT-qPCR data in our current study. The expression of HaDof04 and HaDof43 were not detected in any samples, which implied that they may be gradually undergoing pseudogenization process. Some HaDof genes, such as HaDof25 and HaDof30 , showed responsiveness to exogenous plant hormones, such as kinetin, brassinosteroid, auxin or strigolactone, while others like HaDof15 and HaDof35 may participate in abiotic stress resistance of sunflower seedling. Our study represents the initial step towards understanding the phylogeny and expression characterization of sunflower Dof family genes, which may provide valuable reference information for functional studies on hormone response, abiotic stress resistance, and molecular breeding in sunflower and other species. [ABSTRACT FROM AUTHOR]

The basic helix-loop-helix (bHLH) transcription factors play important roles in many processes such as plant growth, metabolism and response to biotic/abiotic stresses. Sunflower (Helianthus annuus) is a major oil crop, cultivated throughout the world. However, no systematic characterization of bHLH gene members in sunflower (HabHLH) and their functions involved in drought, cadmium tolerance and Orobanche cumana resistance has been reported yet. In this study, 183 HabHLH genes were identified and named according to their chromosomal locations. We classified these proteins into 21 subfamilies by phylogenetic tree analysis. Subsequently, DNA-binding patterns, sequence analysis, duplication analysis and gene structures were analyzed. All of the HabHLH genes were randomly distributed on 17 chromosomes, and 10 pairs of tandem duplicated genes and one pair of segmental duplicated genes were detected in the HabHLH family. Among the duplicated gene pairs, eight pairs of HabHLH genes suffer from positive selection. Moreover, qRT-PCR results revealed significant up-regulated expression of HabHLH024 gene in response to both abiotic (cadmium, drought) and biotic (Orobanche cumana) stresses, suggesting its important functions in response to different stresses. Therefore, HabHLH024 would be the potential candidate gene for the sunflower tolerance breeding. [Display omitted] • A total of 183 bHLH genes were identified in Helianthus annuus L. • There were 21 bHLH subfamilies defined in sunflower. • Tandem duplications contribute to expansion of HabHLH genes. • 56 selected HabHLH s were differentially expressed under biotic and abiotic stresses. • HabHLH024 highly expressed under cadmium, drought, and Orobanche cumana stresses. [ABSTRACT FROM AUTHOR]

CONSTANS-like (COL) genes play crucial roles in the regulation of photoperiodic flowering and responses to biotic and abiotic stresses; however, COL genes in sunflower (HaCOL) have not been extensively studied. In the present study, we identified 22 putative HaCOL genes in the whole genome sequence of sunflower, which were unevenly distributed on 10 chromosomes. The phylogenetic analysis showed that the HaCOLs could be divided into three well-defined groups (groups I, II and III). Group III had the highest number of COL genes among the three tested monocots, while the highest number of COL genes were observed in group I among the five tested dicots. Among all eight species, group II had the fewest COL family members. Segmental duplications contributed greatly to the expansion of this gene family. Furthermore, 11 tissue expression profiles of 22 HaCOL genes were analyzed through RNA-seq, which displayed their tissue-specific expression profiles. In addition, the expression levels of these HaCOL genes were analyzed under hormone, cadmium (Cd), heat, and drought stresses, and the results showed that HaCOL3 , HaCOL6 , and HaCOL19 were more sensitive than other HaCOLs to certain abiotic stresses. Moreover, the duplicated genes conferred important neofunctionalization in response to abiotic stresses. On the basis of our findings, we speculate that this conserved, duplicated and neofunctionalized COL gene family may play pivotal roles in the adaptation of sunflower to adverse environments. • A total of 22 putative CONSTANS-like genes identified in sunflower genome. • Sunflower CONSTANS-like genes could be divided into three well defined groups. • Segmental duplications contribute greatly to the expansion of this gene family. • Duplicated genes confer their novel functions in response to abiotic stresses. • The neofunctionalized sunflower COLs involved in environmental adaptation. [ABSTRACT FROM AUTHOR]