Loss of staminodes in Aquilegia jonesii reveals a fading stamen-staminode boundary

In this study we describe the phenotypic complexity and genetic architecture associated with the loss of staminodes in Jones' columbine, Aquilegia jonesii using Quantitative Trait Locus (QTL) analysis.The modification of fertile stamens into sterile staminodes has occurred independently many times in the flowering plant lineage. In the genus Aquilegia (columbine) and its closest relatives, the two stamen whorls closest to the carpels have been converted to staminodes. In Aquilegia, the only genetic analyses of staminode development have been reverse genetic approaches revealing that B-class floral identity genes are involved. A. jonesii, the only species of columbine where staminodes have reverted to fertile stamens, allows us to explore the genetic architecture of staminode development using a forward genetic approach. We performed QTL analysis using an outcrossed F2 population between A. jonesii and a horticultural variety that makes fully developed staminodes, A. coerulea "Origami". Our results reveal a polygenic basis for staminode loss where the two staminode whorls are under some level of independent control. We also discovered that staminode loss in A. jonesii is not complete, in which staminode like traits sometimes occur in the inner fertile stamens, potentially representing a fading boundary of gene expression. The QTLs identified in this study provide a map to guide future reverse genetic and functional studies examining the genetic basis and evolutionary significance of this trait.

本研究通过数量性状基因座(Quantitative Trait Locus, QTL)分析，解析了琼斯耧斗菜（Aquilegia jonesii）中退化雄蕊丢失相关的表型复杂性与遗传结构。可育雄蕊向不育退化雄蕊的演化转变在被子植物演化支中独立发生过多次。在耧斗菜属（Aquilegia）及其近缘类群中，靠近心皮的两轮雄蕊已特化为退化雄蕊。此前针对耧斗菜属退化雄蕊发育的遗传分析仅采用反向遗传学手段，结果表明B类花同源异型基因参与其中。琼斯耧斗菜（A. jonesii）是目前已知唯一一种退化雄蕊恢复为可育雄蕊的耧斗菜属物种，这为我们通过正向遗传学手段探究退化雄蕊发育的遗传结构提供了绝佳研究体系。本研究以琼斯耧斗菜与具有完全发育退化雄蕊的园艺品种蓝花耧斗菜（A. coerulea "Origami"）杂交得到的异交F2群体为材料，开展了QTL分析。研究结果表明，退化雄蕊丢失的遗传基础为多基因调控，且两轮退化雄蕊的发育分别受到一定程度的独立调控。此外，本研究还发现琼斯耧斗菜的退化雄蕊丢失并非完全彻底：在内层可育雄蕊中偶尔会出现类退化雄蕊的性状，这可能代表了基因表达边界的渐退现象。本研究鉴定得到的QTL位点可为未来开展反向遗传学与功能研究提供指引，以解析该性状的遗传基础与演化意义。