2017 ASHS Annual Conference

The life cycle of annual flowering plants is marked by several distinct developmental phases. It initiates with seed germination, goes through juvenile to adult and reproductive phase transitions, and ends up with flowering, embryogenesis and seed maturation. The flowering time and seed germination are two of most critical developmental phase transitions; both of them are coordinately regulated by genetic and environmental factors to greatly affect the success of establishment, reproduction, colonization and adaptation of plant populations. The DELAY OF GERMINATION1 (DOG1) gene is involved in regulating seed dormancy in response to temperature and has also been associated genetically with pleiotropic flowering phenotypes across diverse Arabidopsis thaliana accessions and locations. Here we show that DOG1 can regulate both seed dormancy and flowering times in lettuce (Lactuca sativa) and Arabidopsis through an influence on levels of microRNAs miR156 and miR172. In lettuce, suppression of LsDOG1 expression enabled seed germination at high temperature and promoted early flowering in association with reduced miR156 and increased miR172 levels. Overexpression MIR156 under CaMV35S promoter in lettuce caused extremely late flowering, whereas sequestering miR156 resulted in early flowering and loss of lettuce seed thermoinhibition. In Arabidopsis, higher miR156 levels resulting from overexpression of the MIR156 gene enhanced seed dormancy and delayed flowering. These phenotypic effects, as well as conversion of MIR156 transcripts to miR156, were compromised in DOG1 loss of function but enhanced in DOG1 gain of function in mutant seeds. Over-expression of MIR172 reduced seed dormancy and promoted early flowering in Arabidopsis, and the effect on flowering required functional DOG1. Transcript levels of several genes associated with miRNA processing were consistently lower in dry seeds of Arabidopsis and lettuce when DOG1 was mutated or its expression was reduced; in contrast, transcript levels of these genes were elevated in a DOG1 gain of function mutant. Our results reveal a previously unknown linkage between two critical developmental phase transitions in the plant life cycle through a DOG1-miR156-miR172 interaction.