Abstract
Rice seed germination is a critical step that determines its entire life circle, with seeds failing to germinate or pre-harvest sprouting both reduce grain yield. Nevertheless, the mechanisms underlying this complex biological event remain unclear. Previously, gibberellin has been shown to promote seed germination. In this study, a delayed seed germination rice mutant was obtained through screening of the EMS induced mutants. Besides of delayed germination, it also shows semi-dwarfism phenotype, which could be recovered by exogenous GA. Through re-sequencing on the mutant, wild-type and their F2 populations, we identified two continuous mutated sites on ent-kaurene oxidase 1 (OsKO1) gene, which result in the conversion from Thr to Met in the cytochrome P450 domain. Genetic complementary analysis and enzyme assay verified that the mutations in OsKO1 gene block the biosynthesis of GA and result in the defect phenotypes. Further analyses proved that OsKO1 could catalyze the reaction from ent-kaurene into ent-kaurenoic acid in GA biosynthesis mainly at seed germination and seedling stages, and the mutations decrease its activity to catalyze the step from ent-kaurenol to ent-kaurenoic acid in this reaction. Transcriptomic and proteomic data indicate that the defect on GA biosynthesis decreases its ability to mobilize starch and attenuate ABA signaling, therefore delay the germination process. The results provide some new insights into both GA biosynthesis and seed germination regulatory pathway in rice.
Highlights
Rice is one of the main cereal grains that feed the world population
Synchronized seed germination upon the stimuli of exogenous environmental factors is critical for its production
The exogenous factors are mediated by endogenous factors, including gibberellins
Summary
Rice is one of the main cereal grains that feed the world population. Rice seed with its independent role as a new generation could provide itself with enough reserves until the establishment of new seedling [1]. Seed germination, which starts with water absorption by the dry seed and ends at radicle protrusion, is controlled by the crosstalk among various phytohormones and environmental stimuli. ABA controls storage reserves accumulation, and induces the expression of late embryogenesis abundant proteins (LEAs) that accumulated during seed maturation to protect seeds against desiccation. Based on the studies in Arabidopsis, it is known that series transcription factors form a cascade in ABA signaling pathway to control seed germination in which ABI1 and ABI2 are two homologous phosphatases that negatively regulate ABI3. ABI3 is a transcription activator that will be degraded by the recognition of AIP2, an E3 ligase ABI3
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