Abstract
Seed germination is the first step for seed plants to initiate a new life cycle. Light plays a predominant role in promoting seed germination, where the initial phase is mediated by photoreceptor phytochrome B (phyB). Previous studies showed that phytochrome-interacting factor1 (PIF1) represses seed germination downstream of phyB. Here, we identify a positive regulator of phyB-dependent seed germination, long hypocotyl in far-red1 (HFR1). HFR1 blocks PIF1 transcriptional activity by forming a heterodimer with PIF1 that prevents PIF1 from binding to DNA. Our whole-genomic analysis shows that HFR1 and PIF1 oppositely mediate the light-regulated transcriptome in imbibed seeds. Through the HFR1-PIF1 module, light regulates expression of numerous genes involved in cell wall loosening, cell division, and hormone pathways to initiate seed germination. The functionally antagonistic HFR1-PIF1 pair constructs a fail-safe mechanism for fine-tuning seed germination during low-level illumination, ensuring a rapid response to favorable environmental changes. This study identifies the HFR1-PIF1 pair as a central module directing the whole genomic transcriptional network to rapidly initiate light-induced seed germination.
Highlights
Seeds play an essential role in the successful colonization of land for angiosperms
To investigate the role of HYPOCOTYL IN FAR-RED1 (HFR1) in seed germination, we examined the phenotypes of mutant hfr1-201 in phytochrome B (phyB)-dependent seed germination
Overexpressing green fluorescent protein (GFP)-tagged HFR1 in the hfr1 background (HFR1-GFP/ hfr1) rescued the seed germination defect of hfr1 and restored the germination frequency to wild-type levels. These results indicate that HFR1 positively regulates phyB-dependent seed germination
Summary
Seeds play an essential role in the successful colonization of land for angiosperms. Upon maturation, the plant embryo stops growth and seed dormancy is established. The Pr form of phytochrome is converted to the Pfr form to initiate red light– regulated plant development (Quail, 2002; Chen et al, 2004). PhyA and phyB are the main receptors of light-induced seed germination and other PHYs (phyC to E) play minor roles during the process (Lee et al, 2012). Recent study showed that canopy light suppresses phyB-dependent germination in the endosperm and activates phyA-dependent germination in the embryo, which involves spatial abscisic acid (ABA) signaling responses (Lee et al, 2012). The different roles of phyA and phyB are important for the plant’s ability to adapt to different light conditions during germination
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