The role of the oxylipin OPDA in the seasonal sensitivity of seed dormancy

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Seasonal plant growth, typically initiated with the onset of bud burst or seed germination in the spring and terminated with the onset of dormancy in the progression through autumn to winter, is a well recognised natural phenomenon that can affect annual atmospheric gas exchange on a global scale. Environmental cues such as day-length and temperature are well known to directly affect plant growth and development, but much less is known about how such cues are used by plants to establish dormancy in advance of major seasonal change. There is a growing interest in understanding the underlying mechanism responsible for these predictive responses, not least because such knowledge will help us to predict how wild plants and crops will respond to environmental change. We have recently made two important discoveries that point to a lipid signalling molecule, OPDA, having a central role in controlling dormancy in seeds and being involved in the transfer of information governing seasonal growth control from one generation to the next. Both of these discoveries were made in the model plant species Arabidopsis thaliana, but knowledge gained will be applicable to other plant species. In the first discovery we found that elevated OPDA is responsible for increased seed dormancy in several Arabidopsis mutants. Exogenous OPDA application inhibits germination and we have evidence to show it involves at least one downstream target, a transcription factor protein called ABI5 that increases in abundance in the presence of OPDA and is essential for the OPDA imposed dormancy in beta-oxidation mutant seeds. In the second discovery we found that the day-length in which Arabidopsis plants are grown has a dramatic effect on the levels of OPDA in vegetative tissues and the dormancy state of seeds in the next generation. This effect on OPDA and seed dormancy is dependent on a protein called Flowering Locus T (FT) that is involved in regulating expression in vegetative tissues of a key gene involved in the synthesis of OPDA. A major question that now needs to be addressed is how the 'memory' of day-length in vegetative tissues is transmitted to the next generation and manifested in the dormancy status of seeds. Our preliminary studies indicate that OPDA plays a central role in the memory retention across generations from vegetative material to seeds. Furthermore, other recent work suggests a similar mechanism involving the FT protein controls dormancy in vegetative buds in perennial species such as poplar trees. The aim of our research is to establish the mechanism by which environmental signals influence seasonal growth by modification of the dormancy state of vegetative buds and seeds. To achieve this aim we will first establish how the FT protein regulates OPDA levels in vegetative tissues and establish the mechanism by which FT-dependent information is transferred from one generation to the next. The most likely mechanism is one involving epigenetic non-permanent modification of DNA that can affect gene expression and hence traits and phenotypes from one generation to the next. In parallel with this work we will establish how environmental signals during seed development influence dormancy state and OPDA levels. We will also elucidate the signal transduction pathway involved in the OPDA mediated control of seed dormancy. Finally, building on our remarkable observation that the environment experienced during seed set influences the growth rate of plants derived from that seed, we will investigate if an epigenetic OPDA-dependent memory of the seed maturation environment is involved. The outputs of this research will impact on the way we predict how plant ecosystems respond to environmental change. It may also impact on the development of improved agronomic practice for the production of seeds that are less dormant and/or give rise to crops that grow more vigorously.