Alterations in gene expression and DNA during loss and re-establishment of desiccation-tolerance in germinating and germinated Medicago truncatula seeds

This study investigated the expression of various genes during loss and re-establishment of desiccation tolerance (DT) in germinating and germinated Medicago truncatula Gaertn. 'Jemalong' A17 seeds. Osmotic treatment with polyethylene glycol (PEG) substantially re-established DT in germinated seeds with a protruded radicle up to 2 mm long, just before the resumption of the cell cycle. Real-time polymerase chain reaction (PCR) with gene-specific primers for M. truncatula showed that gene expression at the transcriptional level was clearly affected by germination, and responded to osmotic treatment and dehydration. Stress-related genes (i.e. EM6, Per1 and sHSP) were downregulated during germination and upregulated by osmotic treatment, suggesting their involvement in the loss and reacquisition of DT in seeds. Cell cycle-associated genes (i.e. CDC2a) and cytoskeleton-associated genes (i.e. ACT and TUB) were upregulated during germination and were affected in various ways by PEG treatment. Upon dehydration, the mRNA levels of these genes decreased. No clear correlation was found between the expression of developmental genes (i.e. AB13, LEC1 and CTS) and DT.