The extraordinary diversity of angiosperms is facilitated by their flowers, which promote outcrossing. Outcrossing maintains genetic variation and is essential for hybrid seed production. Crop production however is often facilitated by a combination of self- and cross-pollination. Thus, the ability of plant breeders to generate plants that preferentially self- or cross-pollinate is extremely useful, but currently limited to a small number of crops. Two related crops, lettuce and sunflower, have very similar floral anatomy. Despite these similarities, lettuce is exclusively self-pollinating, while sunflower depends upon cross-pollination by insects. Using lettuce and sunflowers as models, a diverse team of researcher (UC Davis: PI Harmer; UC Berkeley: co-PI Blackman; Iowa State: co-PI Barb) investigate how internal and external factors interact to generate these distinct reproductive strategies in lettuce and sunflower. Specifically, the investigators use genomic, physiological, and quantitative genetic approaches to better understand how the precise timing of late stage floral development promotes self- or cross-pollination. A better understanding of the regulation of these processes is likely to lead to new approaches to modify the frequency of self- and cross-pollination in crop species, providing important new tools for breeders. Given the anticipated challenges of future climates and observed declines in both wild and managed pollinator populations, a better understanding of the traits underlying plant mating strategies and their modulation by environmental factors is key to future agronomic improvements and global food security. The proposed research also provides interdisciplinary training for the next generation of scientists to thrive in an era of highly integrative research.

Protandry, the condition in which a single flower is first male and then female, is a reproductive strategy that promotes out-crossing in many plant species including cultivated sunflower. Preliminary data has shown that protandry is regulated both by the circadian clock and the environment. In lettuce, which is almost entirely self-pollinating, floret morphology is similar to cultivated sunflower, but the male and female phases occur simultaneously. These two crops, sunflower and lettuce will be used as models to define how environmental and internal cues direct floral organ growth to promote out-crossing or self-pollination. Comparative transcriptomic studies are used to identify pathways controlling the timing of late-stage floral development. The team uses quantitative genomic studies to uncover the underlying architecture of the genetic variation that affects floret maturation and discern its impact on self- and cross-pollination. Open field and pollinator cage studies are used to assess the importance of the timing of late floral development (anthesis) relative to other floral traits in the reproductive strategies of out-crossing versus selfing. These studies highlight targets for improving yield under suboptimal pollinator activity and may facilitate development of inbred lines that are more attractive to pollinators, potentially leading to substantial cost savings by hybrid seed producers. High school students, undergraduates, and community volunteers contribute to discovery-based research in the classroom, lab, field, and at the UC Botanical Garden. Undergraduate interns are recruited from programs that connect underrepresented groups in STEM fields with researchers. These efforts also provide excellent teaching opportunities for postdoctoral scholars and graduate students supported by the project.

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.

National Science Foundation (NSF)
Division of Integrative Organismal Systems (IOS)
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Kimberly Gallagher
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University of California Davis
United States
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