BRC-BIO: The transcriptomics of environmentally-controlled differentiation into male or female in plants

Plants reproduce via male and female functions much like animals do. Differently from animals, however, most plants (~90%) combine male and female function in one individual. Even though less than 10% of plant species have separate males and females, this plant mating system has evolved repeatedly in the history of green plants and provides an opportunity to understand its evolution. Moreover, many economically important crops have separate males and females, and often the male or the female is more valuable than the other (e.g., female holly, male gingko), and they can be difficult to distinguish before maturity. In other situations, keeping males and females separate and stable (e.g., female Cannabis, female hops) is necessary to maintain the quality of a product. Despite the importance of this aspect of plant biology economically we know little about factors that determine this expression in plants. This project will research a special group of plants that exhibit separate males and females – those for which the environment controls the expression of male or female function. Chromosomes that determine male or female flower types are rare in plants and species where the environment plays a strong role have the ability to express either male or female flowers, and change from one to the other, during their lives. Changes in gene expression is the most likely mechanism controlling this phenotype in these species thus, this study examines the relationship between gene expression and floral development in maples and makes comparisons to other plant species with different plant mating systems. Understanding more about how gene expression relates to expression of male versus female flowers will help make more economical decisions and plan for population stability in the face of climate change. This project also involves the development of Course-based Undergraduate Research Experiences that include both field elements and training in modern genetic techniques and analysis. It also involves local outreach with a focus on evolutionary biology.

Historically several mechanisms that determine male versus female function in organisms has been categorized: genetic, social, temperature dependent, and environmental. This division has resulted in primarily ecologically-based research of species with suspected environmental determination and reinforced a false dichotomy between genetics and environment. This project investigates the transcriptomic underpinnings of environmentally-based plasticity in floral function and seeks answers to the following questions. 1. Are there differences in the amount and kind of gene expression associated with the expression of floral type? 2. To what extent does the transcriptome change during floral development? 3. How similar is the transcriptomic profile of species with this plasticity in comparison to other species? Is it more similar to those exhibiting dioecy or monoecy? Through this work new understanding of how gene activation and activity responds to the environment to shape floral phenotype will obtain. This understanding is becoming more critical with a changing climate. Furthermore, the proposed research addresses long-held questions on the evolution of plant mating systems. Although environmental control of floral phenotype is frequently mentioned as a potential pathway to dioecy, no studies have explored how transcriptomically similar these species are to those with monoecious or dioecious mating systems. This inhibits our understanding of the route to dioecy, a major and repeated evolutionary transition in plants. Similar evolutionary transitions in animals happened too infrequently and too far back in evolutionary time to facilitate experimental investigation, so if we wish to understand how and why females and males originated, our best chance may reside in the study of plants.

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.