Abstract
The Arabidopsis protein DELAY OF GERMINATION 1 (DOG1) is a key regulator of seed dormancy, which is a life history trait that determines the timing of seedling emergence. The amount of DOG1 protein in freshly harvested seeds determines their dormancy level. DOG1 has been identified as a major dormancy QTL and variation in DOG1 transcript levels between accessions contributes to natural variation for seed dormancy. The DOG1 gene is alternatively spliced. Alternative splicing increases the transcriptome and proteome diversity in higher eukaryotes by producing transcripts that encode for proteins with altered or lost function. It can also generate tissue specific transcripts or affect mRNA stability. Here we suggest a different role for alternative splicing of the DOG1 gene. DOG1 produces five transcript variants encoding three protein isoforms. Transgenic dog1 mutant seeds expressing single DOG1 transcript variants from the endogenous DOG1 promoter did not complement because they were non-dormant and lacked DOG1 protein. However, transgenic plants overexpressing single DOG1 variants from the 35S promoter could accumulate protein and showed complementation. Simultaneous expression of two or more DOG1 transcript variants from the endogenous DOG1 promoter also led to increased dormancy levels and accumulation of DOG1 protein. This suggests that single isoforms are functional, but require the presence of additional isoforms to prevent protein degradation. Subsequently, we found that the DOG1 protein can bind to itself and that this binding is required for DOG1 function but not for protein accumulation. Natural variation for DOG1 binding efficiency was observed among Arabidopsis accessions and contributes to variation in seed dormancy.
Highlights
Alternative splicing has an important role in the post-transcriptional regulation of higher eukaryotes, but it was long believed to be of minor significance in plants
The amount of DELAY OF GERMINATION 1 (DOG1) protein in mature seeds correlates with their dormancy level
It has been demonstrated that DOG1 is an important contributor to natural variation for seed dormancy and Arabidopsis accessions vary in their DOG1 levels
Summary
Alternative splicing has an important role in the post-transcriptional regulation of higher eukaryotes, but it was long believed to be of minor significance in plants. At the beginning of this century only 1.5% of the Arabidopsis thaliana genes were estimated being alternatively spliced [1]. Within one decade this fraction went up to 61% [2]. The regulation and function of alternative splicing in plants is still largely unexplored but several examples have demonstrated its functional importance in various processes like photosynthesis, defence responses, the circadian clock, hormone signalling, flowering time, and metabolism [5,6,7,8]. A few examples have shown a role of alternative splicing during seed development and germination. The PHYTOCHROME INTERACT ING FACTOR 6 gene is alternatively spliced during seed development and one of its two splice forms, PIF6-β influences germination potential [11]
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