Genome wide association mapping of floral traits in cultivated sunflower (Helianthus annuus)

Floral morphology and pigmentation are both charismatic and economically relevant traits associated with cultivated sunflower (Helianthus annuus L.). Recent work has linked floral morphology and pigmentation to pollinator efficiency and seed yield. Understanding the genetic architecture of such traits is essential for crop improvement, and gives insight into the role of genetic constraints in shaping floral diversity. A diversity panel of 288 sunflower genotypes was phenotyped for a variety of morphological, phenological, and color traits in both a greenhouse and a field setting. Association mapping was performed using 5788 SNP markers using a mixed linear model approach. Several dozen markers across ten linkage groups were significantly associated with variation in morphological and color trait variation. Substantial trait plasticity was observed between greenhouse and field phenotyping, and associations differed between environments. Color traits mapped more strongly than morphology in both settings, with markers together explaining 16% of petal carotenoid content in the greenhouse, and 17% and 24% of variation in disc anthocyanin presence in the field and greenhouse, respectively. Morphological traits like disc size mapped more strongly in the field, with markers together explaining up to 19% of disc size variation. Loci identified here through association mapping within cultivated germplasm differ from those identified through biparental crosses between modern cultivated sunflower and either its wild progenitor or domesticated landraces. Several loci lie within genomic regions involved in domestication. Differences between phenotype expression under greenhouse and field conditions highlight the importance of plasticity in determining floral morphology and pigmentation.

花形态与色素性状既是极具研究吸引力的性状，也是与栽培向日葵（Helianthus annuus L.）相关的经济性状。已有研究将花形态与色素性状与传粉者效率及种子产量建立了关联。解析这类性状的遗传架构，对作物遗传改良至关重要，同时也能帮助我们理解遗传限制在塑造花类多样性中所扮演的角色。本研究针对288份向日葵基因型构成的多样性关联群体，在温室与田间两种环境下，对其多项形态、物候及颜色性状开展了表型鉴定。本研究采用混合线性模型方法，基于5788个单核苷酸多态性（SNP）标记开展关联作图分析。在10个连锁群上共有数十个标记与形态及颜色性状的变异存在显著关联。研究观察到温室与田间表型鉴定环境下存在显著的性状可塑性，且不同环境下的关联位点存在差异。在两种环境中，颜色性状的关联定位效果均优于形态性状：在温室环境下，相关标记联合可解释花瓣类胡萝卜素含量16%的变异；在田间与温室环境下，花盘花青素存在与否的变异分别有17%与24%可由相关标记解释。而花盘大小等形态性状则在田间环境下的定位效果更佳，相关标记联合最多可解释花盘大小19%的表型变异。本研究在栽培种质资源中通过关联作图鉴定到的位点，与通过现代栽培向日葵与其野生祖先种或驯化地方品种进行双亲杂交所鉴定到的位点存在差异。部分位点位于与驯化过程相关的基因组区域内。温室与田间环境下的表型表达差异，凸显了性状可塑性在决定花形态与色素性状中的重要作用。