Excellence in Research: Developing a Model System for Studying the Determinants of Flower Morphology in Tropical Dioecious Trees

In many plant species, one can find presence of male and female flowers on separate plants or on same plants or single flowers carrying both the stamens (male) and pistil (female) parts. The interplay between genetics and the environment in determining the flower type and development of floral organs in such plants remains largely uninvestigated. To study this phenomenon, the project team will use Coccoloba diversifolia (pigeonplum), a native of neotropical coastal areas of Southern Florida, Caribbean, Southern Mexico and Central America. It is an important native tropical tree and shows a varying degree of flower patterns mentioned above. The team will sequence the genome of this plant species and profile the genetics and flowering patterns found in a wild population to identify the regions of genome that play a role in regulating the development of flowers and floral organs. The proposed experiments, data collection and analyses will provide an excellent opportunity and source material to train the graduate and undergraduate students in genomics, bioinformatics, biological data science and conservation. Among dioecious taxa, the factors and mechanisms determining which biological individuals are pistillate and which are staminate are still not well understood. In a small percentage of cases, heteromorphic chromosomes have been identified as one major determinant. In other cases, environmental factors have been identified as major determinants. Yet even these cases appear not to identify strict determinants. Moreover, the biological systems in which these phenomena are studied, have been overwhelmingly herbaceous and temperate. The project looks to examine the interplay of genetics and the environment in the determination of pistillate and staminate individuals in a tropical tree with variable floral expression. The project will (1) assemble and annotate the complete nuclear genome of the study taxon Coccoloba diversifolia using a combination of short- and long-read DNA sequencing along with proximity ligation, (2) identify the genetic regions contributing to the determination of pistillate or staminate individuals through population sampling, shallow whole genome shotgun sequencing and the identification of morphology-specific reads, and (3) assess the contribution of environment in determining flower morphology through the documentation of flower morphology ratios in relation to environmental conditions for populations of C. diversifolia in South Florida. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.