Table_4_Characterization of Frond and Flower Development and Identification of FT and FD Genes From Duckweed Lemna aequinoctialis Nd.XLSX

Duckweeds (Araceae: Lemnoideae) are aquatic monocotyledonous plants that are characterized by their small size, rapid growth, and wide distribution. Developmental processes regulating the formation of their small leaf-like structures, called fronds, and tiny flowers are not well characterized. In many plant species, flowering is promoted by the florigen activation complex, whose major components are florigen FLOWERING LOCUS T (FT) protein and transcription factor FD protein. How this complex is regulated at the molecular level during duckweed flowering is also not well understood. In this study, we characterized the course of developmental changes during frond development and flower formation in Lemna aequinoctialis Nd, a short-day plant. Detailed observations of frond and flower development revealed that cell proliferation in the early stages of frond development is active as can be seen in the separate regions corresponding to two budding pouches in the proximal region of the mother frond. L. aequinoctialis produces two stamens of different lengths with the longer stamen growing more rapidly. Using high-throughput RNA sequencing (RNA-seq) and de novo assembly of transcripts from plants induced to flower, we identified the L. aequinoctialis FT and FD genes, whose products in other angiosperms form a transcriptional complex to promote flowering. We characterized the protein-protein interaction of duckweed FT and FD in yeast and examined the functions of the two gene products by overexpression in Arabidopsis. We found that L. aequinoctialis FTL1 promotes flowering, whereas FTL2 suppresses flowering.

浮萍（天南星科：浮萍亚科）为水生单子叶植物，以体型微小、生长迅速、分布广泛为典型特征。目前，针对其被称为叶状体（frond）的小型叶状结构与微小花朵的形成发育调控过程，尚未得到充分阐释。在多数植物物种中，成花素激活复合物（florigen activation complex）可促进开花进程，该复合物的核心组分为成花素FLOWERING LOCUS T（FT）蛋白与转录因子FD蛋白。而浮萍开花过程中该复合物的分子调控机制，同样尚未得到清晰解析。本研究以短日照植物稀脉浮萍（Lemna aequinoctialis Nd）为实验材料，系统表征了其叶状体发育与花形成过程中的发育变化历程。对叶状体与花发育的详细观察显示，叶状体发育早期的细胞增殖活动十分活跃，可观测到对应于母叶状体近端区域两个芽囊的独立增殖区域。稀脉浮萍可产生两枚长度不等的雄蕊，且较长雄蕊的生长速度更快。本研究通过高通量RNA测序（RNA-seq）与开花诱导植株转录本的从头组装（de novo assembly），成功鉴定出稀脉浮萍的FT与FD基因——在其他被子植物中，这两个基因的编码产物可形成转录复合物以促进开花。我们在酵母体系中表征了浮萍FT与FD的蛋白质相互作用，并通过在拟南芥（Arabidopsis）中过表达这两个基因产物来检测其功能。研究发现，稀脉浮萍的FTL1可促进开花，而FTL2则抑制开花。