Beta vulgaris Transcriptome cold-induced secondary dormancy

The dynamic behaviour of seeds in soil seed banks depends on their ability to act as sophisticated environmental sensors which integrate spatiotemporal information such as ambient temperature. Through mechanisms of secondary dormancy seeds adjust their sensitivity thresholds for germination to the full range of seasonal and more immediate environmental conditions. Here we show that prolonged incubation of sugar beet fruits at low temperature (chilling at 5 degrees Celsius , generally known to release seed dormancy of many species) can induce secondary nondeep physiological dormancy of apparently nondormant crop species. The physiological and biophysical mechanisms underpinning this cold-induced secondary dormancy include the chilling-induced accumulation of abscisic acid (ABA) in the seeds, a reduction in the embryo growth potential and a block in weakening of the endosperm covering the embryonic root. A transcriptome analysis revealed distinct gene expression patterns in the different temperature regimes and upon secondary dormancy induction and maintenance. The chilling caused reduced expression of cell wall remodelling protein genes required for embryo cell elongation growth and endosperm weakening, as well as increased expression of seed maturation genes such as for late embryogenesis abundant proteins. In agreement with the importance of the hormonal network in the temperature-dependent control of these programmes, genes involved in ABA, ethylene and gibberellin metabolism and signalling were differentially expressed. A model integrating the ABA-signalling and master regulator expression with the temperature-control of seed dormancy and maturation programmes is proposed. The revealed mechanisms of the cold-induced secondary dormancy are important for a climate-smart agriculture and food security.