Format: ORAL

Aniket Sengupta and Dianella Howarth

Biological Sciences, St. John’s University, New York, USA

An ongoing question in biology is how gene duplication and changes in gene expression may be associated with morphological shifts. One major innovation in plants is the development of ovules and seeds, traits that evolved in the ancestor of all seed plants. Within seed plants, flowers and fruits are synapomorphies arising within angiosperms, while gymnosperms retain the ancestral absence of these structures. Known floral patterning transcription factors RADIALIS and DIVARICATA are closely related MYB proteins whose competitive interaction is associated with the development of carpels/fruits and the establishment of bilateral symmetry in zygomorphic flowers. RADIALIS has been described as a silencing peptide that is a truncated paralog of DIVARICATA. Through a Bayesian phylogenetic approach, we demonstrate DIVARICATA genes underwent two rounds of duplications at the base of vascular plants forming three clades: DIV-A, DIV-B, and DIV-C. We show that RADIALIS genes evolved from DIV-C genes at the base of seed plants through a premature stop codon that was likely generated by a single-base substitution. This suggests that the RADIALIS-DIVARICATA competitive interaction likely evolved once, at the base of seed plants. We also surveyed the expression pattern of these genes for the first time in a gymnosperm, Ginkgo biloba. We find that Ginkgo biloba RADIALIS genes are expressed widely but often have higher expression in reproductive organs, especially in megasporangia. This is particularly interesting given that the megasporangium is the evolutionary precursor of carpels/fruits. A key innovation associated with megasporangia of seed plants is that they enclose ovules or seeds. Our work provides suggestive evidence that the evolution of seed habit and the later origin of fruits may be associated with the origin of the silencing peptide RADIALIS.