Abstract
Seeds characteristics such as germination ability, dormancy, and storability/longevity are important traits in agriculture, and various genes have been identified that are involved in its regulation at the transcriptional and post-transcriptional level. A particularity of mature dry seeds is a special mechanism that allows them to accumulate more than 10,000 mRNAs during seed maturation and use them as templates to synthesize proteins during germination. Some of these stored mRNAs are also referred to as long-lived mRNAs because they remain translatable even after seeds have been exposed to long-term stressful conditions. Mature seeds can germinate even in the presence of transcriptional inhibitors, and this ability is acquired in mid-seed development. The type of mRNA that accumulates in seeds is affected by the plant hormone abscisic acid and environmental factors, and most of them accumulate in seeds in the form of monosomes. Release of seed dormancy during after-ripening involves the selective oxidation of stored mRNAs and this prevents translation of proteins that function in the suppression of germination after imbibition. Non-selective oxidation and degradation of stored mRNAs occurs during long-term storage of seeds so that the quality of stored RNAs is linked to the degree of seed deterioration. After seed imbibition, a population of stored mRNAs are selectively loaded into polysomes and the mRNAs, involved in processes such as redox, glycolysis, and protein synthesis, are actively translated for germination.
Highlights
The control of seed germination is an important factor for successful agricultural production as it affects early seedling growth, preharvest sprouting/dormancy, and longevity
This demonstrated that protein synthesis in the early phase of germination uses pre-existing mRNA templates that are stored in mature dry seeds
Transcripts of GA 20-oxidase and GA 3-oxidase involved in GA biosynthesis were not detected in the microarray analysis of dry Arabidopsis seeds, their levels increased after seed imbibition [51], suggesting that mRNAs required for GA biosynthesis are not sufficiently abundant in mature dry seeds to stimulate germination
Summary
The control of seed germination is an important factor for successful agricultural production as it affects early seedling growth, preharvest sprouting/dormancy, and longevity (storability). The molecular basis of this regulation has been studied for many years with a landmark discovery made in the 1960s, when de novo protein synthesis was observed in germinating cotton seeds even if transcription was inhibited during imbibition [1,2] This demonstrated that protein synthesis in the early phase of germination uses pre-existing mRNA templates that are stored in mature dry seeds. Some of these ‘stored mRNAs’ are referred to as ‘long-lived mRNAs’ because they remain translatable for long periods, even if the seeds are exposed to stressful conditions. This review outlines the latest findings on stored mRNAs, focusing on their physiological role in seed germination
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