Transcriptional activity during seed imbibition is conserved, robust and required for germination

In most plants, germination begins with the reactivation of metabolism during water uptake by the desiccated seed. Notably, Pol II transcription is hypothesised not to be required for early germination, as seeds appear to initially rely on stored mRNAs produced during their maturation. Here, we show that efficient blocking of Pol II transcription completely stops germination in Arabidopsis seeds. Pol II activity is initiated early and is widespread, following expression and Pol II binding patterns established during seed drying. Our findings suggest that the earliest transcriptional phase relies on pre-existing protein factors. The transcriptional programme initiated during water uptake is robust across diverse imbibition conditions and in seeds matured at different temperatures, and is conserved in rapeseed (Brassica napus). Only after the successful completion of this initial phase and the passing of the translation-dependent checkpoint do seeds activate genes that lead to germination. Our results redefine the role of transcription in seed germination and highlight a conserved pattern of early transcriptional activation.