Spatiotemporal transcriptome atlas of water lily floral organogenesis provide insight to the evolutionary origin of novel traits of angiosperms [Spatial Transcriptomics]

Petals are a key evolutionary innovation of flowers that reshaped plant-pollinator interactions and underlie the dominance of angiosperms in terrestrial ecosystems, yet their evolutionary origin remains debated as the morphological inferences rarely connect directly to the regulatory programs inferred from extant flowering plants. We employed spatial transcriptome sequencing on serial floral buds of the basal angiosperm Nymphaea colorata, producing a spatiotemporal atlas of cell states during primordium initiation and the subsequent formation of tepals (sepals and petals), stamens and carpels.

Our analyses identified multiple meristematic cell populations organized hierarchically at the floral base, with one population give rise to both initiating petals (or inner tepals) and stamens whereas a second population forms carpel primordia. Developmental trajectory reconstruction based on thousands of tissue-preferentially expressed genes uncovers a continuous fate transition from stamen primordia via developing stamens to inner tepals undergoing morphogenesis.