Genetic mapping of sexually dimorphic volatile and non-volatile floral secondary chemistry of a dioecious willow

Authors: KEEFOVER-RING, KENNITH - University Of Wisconsin; Carlson, Craig; HYDEN, BRENNAN - Cornell University; AZEEM, MUHAMMAD - University Of Wisconsin; SMART, LAWRENCE - Cornell University

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2022
Publication Date: 6/17/2022
Citation: Keefover-Ring, K., Carlson, C.H., Hyden, B., Azeem, M., Smart, L. 2022. Genetic mapping of sexually dimorphic volatile and non-volatile floral secondary chemistry of a dioecious willow. Journal of Experimental Botany. 73(18):6352-6366. https://doi.org/10.1093/jxb/erac260.
DOI: https://doi.org/10.1093/jxb/erac260

Interpretive Summary: Species of different sexes are common in animals, but rare in flowering plants. Plants with separate male and female plants account for only 5% of all flowering plants, but are present across most flowering plant groups. There is a lack of knowledge of how different plants evolved separate sexes and what traits are unique to male and female plants. In willow, a bioenergy crop, we find that male and female plants often grow at different rates and have different growth habits, so knowledge of sex-specific differences is important for breeding. In a diverse willow population, we identified chemical compounds which were present in one sex but not the other. Many of the chemicals identified function in plants to both attract and defend from invasion of different insects. In addition, we identified genes most likely to be responsible for chemical differences. This research contributes new research tools as well as new information on how chemical compounds may have aided in the evolution of separate sexes.

Technical Abstract: Secondary chemistry often differs between sexes in dioecious plant species, a pattern attributed to its possible role in the evolution and/or maintenance of dioecy. We used GC-MS to measure floral volatiles emitted from, and LC-MS to quantitate non-volatile secondary compounds contained in, female and male Salix purpurea willow catkins from an F2 family. Using the abundance of these chemicals, we then performed quantitative trait locus (QTL) mapping to locate them on the genome, identified biosynthetic candidate genes in the QTL intervals, and examined expression patterns of candidate genes using RNA-seq. Male flowers emitted more total terpenoids than females, but females produced more benzenoids. Male tissue contained greater amounts of phenolic glycosides, but females had more chalcones and flavonoids. A flavonoid pigment and a spermidine derivative were found only in males. Male catkins were almost twice the mass of females. Forty-two QTL were mapped for 25 chemical traits and catkin mass across 16 of the 19 S. purpurea chromosomes. Several candidate genes were identified, including a chalcone isomerase associated with seven compounds. A better understanding of the genetic basis of the sexually dimorphic chemistry of a dioecious species may shed light on how chemically mediated ecological interactions may have helped in the evolution and maintenance of dioecy.