Integrating floral morphogenesis and transcriptomics in eudicots
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DOI:
https://doi.org/10.22029/jlupub-20923Abstract
Comparative transcriptomics reveals how conserved regulators and flexible gene expression programmes shape the stability and diversity of carpel identity and differentiation. Taking this perspective further, we integrate floral morphogenesis with cross-species transcriptome data across eudicots to test how regulatory change accompanies morphological innovation.An orthogroup (OG) is a set of genes across species that descend from a single gene in their most recent common ancestor (MRCA), encompassing orthologs. On this basis, We mapped OGs to expression profiles and identified conserved and lineage-specific patterns. These patterns are then linked to morphological traits. The findings suggest that a small number of deeply conserved factors are fundamental to carpel development, and that shifts in expression and timing are associated with lineage-specific carpel morphologies.In the first part of this thesis, floral morphogenesis in eudicots is summarized with an emphasis on the origin and diversity of ring meristems. Ring meristems, which generate multiple whorls of stamens, are widespread in Ranunculales and exhibit multiple patterns of initiation. Subsequently, the floral morphogenesis of *Pteridophyllum racemosum* (Papaveraceae, Ranunculales), a sister lineage to the remaining Papaveraceae, is described for the first time. Its floral organs are relatively simple and lack a ring meristem. *P. racemosum* produces flowers with two sepals, four petals in two whorls, four stamens, and a syncarpous gynoecium of two carpels, a combination rare within Papaveraceae but consistent with reconstructions of the family’s ancestral flower.
The second part focuses on transcriptomics of carpel development in eudicots. Transcriptomes of carpels are generated for *Arabidopsis thaliana*, *Eschscholzia californica*, and *Solanum lycopersicum* across four developmental stages. Comparison of OGs revealed that most regulators of carpel development are present in all three species at the genome level, but their expression pattern often differs. Only a few regulators, like *HECATE* (*HEC*) and *FRUITFULL* (*FUL*), follow conserved expression patterns. Detailed mapping from expression of OGs to published regulatory pathways showed that the *NGATHA* (*NGA*) is conserved both in expression and in function, representing a core component of the regulatory network for stigma and style development, while other network, such as those involving polarity establishment, is divergent. These results indicate that carpel development relies on both core regulators and flexible components whose evolutionary role may mediate through expression.
In conclusion, this thesis integrates morphological studies with comparative transcriptomics to investigate the genomics and expression of floral organ evolution in eudicots. The results show that conserved carpel regulators maintained in genome, while flexible expression patterns may be inferred to contribute to differentiation. These results provide valuable gene resources for future functional studies once stable transformation systems are established in non-model systems.