Investigating how internal and external cues coordinate floral organ development and the consequences for plant reproduction
The extraordinary diversity of angiosperms is linked to reproductive strategies that enhance genetic variability by promoting outcrossing. Although outcrossing provides numerous benefits and is essential for hybrid seed production, self-pollination can facilitate efficient crop production. Using two Asteraceae crops as model systems, a diverse team (UC Davis: PI Harmer; UC Berkeley: co-PI Blackman; Iowa State: co-PI Barb) will investigate how external and internal factors interact to modulate these distinct reproductive strategies via influence on the timing of late-stage floral development. In primarily outcrossing sunflower, many individual florets are bundled into a single tightly packed disk, and rings of florets synchronously mature on successive days. Each floret presents pollen one day and exserts its stigmas on the next. Preliminary data show the progress from unopened buds through a male reproductive phase to a female phase is regulated both by the circadian clock and the environment. In lettuce, which is almost entirely self-pollinating, floret morphology is similar, but the male and female phases occur simultaneously. Moreover, unlike sunflower heads, lettuce disks open and close in daily cycles driven by rhythms in corolla elongation. The proposed research will investigate mechanisms that regulate the development of these floral traits to understand how different reproductive strategies emerge and succeed in fluctuating environments. Physiological experiments will define how environmental and internal cues direct floral organ growth to promote outcrossing or selfing. Comparative transcriptomic studies will identify pathways controlling the timing of late-stage floral development. Finally, quantitative genomic studies will reveal the genetic architecture of variation that affects floret maturation and its impact on self- and cross-pollination.