Gene identification and tissue expression analysis inform the floral organization and color in the basal angiosperm Magnolia polytepala (Magnoliaceae)

Main conclusion In Magnolia polytepala , the formation of floral organization and color was attributed to tissue-dependent differential expression levels of MADS-box genes and anthocyanin biosynthetic genes. In angiosperms, the diversity of floral morphology and organization suggests its value in exploring plant evolution. Magnolia polytepala , an endemic basal angiosperm species in China, possesses three green sepal-like tepals in the outermost whorl and pink petal-like tepals in the inner three whorls, forming unique floral morphology and organization. However, we know little about its underlying molecular regulatory mechanism. Here, we first reported the full-length transcriptome of M. polytepala using PacBio sequencing. A total of 16 MADS-box transcripts were obtained from the transcriptome data, including floral homeotic genes (e.g., MpAPETALA3 ) and other non-floral homeotic genes ( MpAGL6 , etc.). Phylogenetic analysis and spatial expression pattern reflected their putative biological function as their homologues in Arabidopsis . In addition, nine structural genes involved in anthocyanin biosynthesis pathway had been screened out, and tepal color difference was significantly associated with their tissue-dependent differential expression levels. This study provides a relatively comprehensive investigation of the MADS-box family and anthocyanin biosynthetic genes in M. polytepala , and will facilitate our understanding of the regulatory mechanism underlying floral organization and color in basal angiosperms.