Abstract
Seed dormancy determines germination timing and contributes to crop production and the adaptation of natural populations to their environment. Our knowledge about its regulation is limited. In a mutagenesis screen of a highly dormant Arabidopsis thaliana line, the reduced dormancy5 (rdo5) mutant was isolated based on its strongly reduced seed dormancy. Cloning of RDO5 showed that it encodes a PP2C phosphatase. Several PP2C phosphatases belonging to clade A are involved in abscisic acid signaling and control seed dormancy. However, RDO5 does not cluster with clade A phosphatases, and abscisic acid levels and sensitivity are unaltered in the rdo5 mutant. RDO5 transcript could only be detected in seeds and was most abundant in dry seeds. RDO5 was found in cells throughout the embryo and is located in the nucleus. A transcriptome analysis revealed that several genes belonging to the conserved PUF family of RNA binding proteins, in particular Arabidopsis PUMILIO9 (APUM9) and APUM11, showed strongly enhanced transcript levels in rdo5 during seed imbibition. Further transgenic analyses indicated that APUM9 reduces seed dormancy. Interestingly, reduction of APUM transcripts by RNA interference complemented the reduced dormancy phenotype of rdo5, indicating that RDO5 functions by suppressing APUM transcript levels.
Highlights
The moment when a seed germinates is a crucial decision during the life cycle of plants because it determines all subsequent events
Several mutants with abolished or reduced seed dormancy were isolated in this mutagenesis screen, among them a nondormant mutant that was later identified as dog1-1 (Bentsink et al, 2006)
Three independent single insertion lines all showed reduced seed dormancy compared with the Col background (Figure 7C). These results indicate a negative relation of Arabidopsis PUMILIO9 (APUM9) transcript levels with seed dormancy, which is consistent with the high APUM9 and APUM11 transcript levels in the nondormant rdo5-1 mutant
Summary
The moment when a seed germinates is a crucial decision during the life cycle of plants because it determines all subsequent events. Seed dormancy is induced during maturation of seeds on the mother plant and released by dry storage (afterripening) or imbibition at low temperatures. A tight control of dormancy is important in many crop species, including rapeseed (Brassica napus), wheat (Triticum spp), barley (Hordeum vulgare), and rice (Oryza sativa). Low levels of dormancy can cause preharvest spouting, which can cause economic losses to cereal production including reductions in seed quantity and quality. Low seed dormancy is required for uniform and fast germination after sowing (Gubler et al, 2005; Holdsworth et al, 2008; Graeber et al, 2012). An improved control of seed dormancy and germination requires understanding of its molecular mechanisms
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