Temperature has a key role in shaping the local environment of plants, and heat information can be picked up by the mother plant or seeds themselves. It is thought that temperature has a large influence over several traits, including seed dormancy – a characteristic resulting in seeds not germinating despite being surrounded by the right conditions. Temperature can therefore ultimately shape the progress a seed will make. Yet the exact method with which the plants integrate temperature information is unknown. The EU-funded MATHCOV project has been unravelling it. “The key aims of this project were to find out how temperature history affects vegetable seed quality, and in particular the germination performance of the seedlings. The developing seed is a complex arrangement of different tissues and we wanted to see which were most important in the process,” says Steve Penfield, head of the Penfield group at the John Innes Centre.
Targeting the endosperm
The group’s previous research had shown the endosperm to be a critical area for the perception of temperature signals. This is a tissue surrounding the embryo produced by double fertilisation in most flowering plants, including brassica, or cabbage plants, valuable crops for human nutrition. “The endosperm plays many roles, including determining seed size and nourishing the embryo, but it also communicates with the other seed tissues via hormone transport,” explains Penfield, MATHCOV project coordinator. MATHCOV investigated how the temperature during seed production controls both germination and seed vigour, and how exactly the endosperm is involved. The team used time-series transcriptomics, a process for studying all messenger RNA molecules in the endosperm. This reflects which genes are active in a tissue at any one time. “We carried out the time-series transcriptomics during seed development to understand the response of the endosperm to changes in temperature that affect seed vigour after germination,” notes Penfield. This information is then translated into a ‘gene network’, a mathematical representation of all the active genes, which can be analysed to reveal similarities and differences in the pattern of activity over time. “In this way we can identify early and late temperature responsive genes, and the so-called hub genes that are core regulators regulating seed germination in our research,” Penfield adds. As a final step, the researchers looked at the changes in gene expression, the process through which information from a gene is used to create proteins. “Study of this so-called epigenetic profile can provide insights into how temperature-related changes in gene expression occur, and how they can continue to affect the performance of seeds after germination – long after the original temperature signal has disappeared,” Penfield explains.
The team found key genes involved in temperature-induced differences. “These genes are involved in abscisic acid metabolism, which plays important roles in controlling seed germination,” says Penfield. The complex data sets produced during the project will benefit seed scientists and seed companies, by showing how to improve seed performance and reliability. “This is increasingly important, as seed raising becomes more automated. In seeding production for field vegetable planting, for instance, or indoor vertical farming,” Penfield concludes.
MATHCOV, seed, germination, temperature, genes, expression, vigour, growth