DOG1 REGULATES BOTH SEED DORMANCY AND FLOWERING THROUGH MicroRNA156
Huo, H.1,2 and Bradford, K.J.2
1Mid-Florida Research and Education Center, University of Florida, Apopka, FL 32703
2Department of Plant Sciences, Seed Biotechnology Center, University of California, Davis, California, USA
Contact: Heqiang Huo, email@example.com
The life cycle of annual flowering plants is marked by distinct developmental phases. It initiates with seed germination and progresses through juvenile, adult, flowering, embryogenesis and seed maturation phase transitions. The transitions from seed dormancy to germination and from adult to flowering are coordinately regulated by genetic and environmental factors as they strongly 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 during seed maturation and has also been associated genetically with pleiotropic flowering phenotypes across diverse Arabidopsis thaliana accessions and locations. Here we show that DOG1 is involved in regulating 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 of MIR156 (gene encoding miR156) under the CaMV35S promoter in lettuce caused extremely late flowering, whereas sequestering miR156 resulted in early flowering and loss of lettuce seed dormancy, as evident in preharvest sprouting. 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 mutants but were enhanced in DOG1 gain-of-function mutants. As miR156 suppresses expression of miR172, bypassing this inhibition by overexpression 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. DOG1 apparently mediates environmental influences during seed maturation involved in the resetting of high miR156/low miR172 levels during embryogenesis that subsequently influence both the progression of seeds from dormancy to germination and of plants from adult to flowering phase.