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Abstract
Seed germination is a complex biological process controlled by various regulators, including phytohormones. Among these, abscisic acid and gibberellic acid inhibit and promote seed germination, respectively. Many studies have addressed the biological roles of auxin in plant growth and development, but very few have considered its role in seed germination. Here, we identified a novel function of the auxin signaling repressor Aux/IAA8 during seed germination. The IAA8 loss-of-function mutant iaa8-1 exhibited delayed seed germination. The phenotype of iaa8-1 was restored by ectopic expression of IAA8. Interestingly, IAA8 accumulated to high levels during seed germination, which was achieved not only by increased protein synthesis but also by the stabilization of IAA8 protein. We also showed that IAA8 down-regulates the transcription of ABSCISIC ACID INSENSITIVE3 (ABI3), a negative regulator of seed germination. Our study, thus strongly suggest that the auxin signaling repressor IAA8 acts as a positive regulator of seed germination in Arabidopsis thaliana.
Highlights
Seed maturation is the final stage of embryogenesis
We provide evidence that IAA8 protein accumulates during seed germination, promoting germination through the inhibition of ABSCISIC ACID INSENSITIVE3 (ABI3) transcription
Exogenous NAA alone did not inhibit seed germination in Col-0 and iaa8-1/IAA8 OX compared to iaa8-1 mutant (Supplementary Figures 3A, B). These results suggest that even upon NAA treatment, small amount of IAA8 protein can be existed in Col-0 and iaa8-1/IAA8 OX, which inhibits ABI3 expression to promote seed germination compared to iaa8-1 mutant seeds
Summary
Seed maturation is the final stage of embryogenesis. The embryo becomes protected by a hard outer cover of dead tissue, the testa, underneath which the endosperm is deposited (Debeaujon et al, 2000). Germination occupies a critical position in the life cycle of seed plants, converting dormant seeds into active seedlings. This process is strictly regulated by genetic and environmental factors (Chen et al, 2008; Bassel et al, 2011; Liu et al, 2013). Lack of dormancy may lead to pre-harvest sprouting (Gubler et al, 2005), resulting in decreased seed longevity (Rajjou and Debeaujon, 2008). It is important to Abbreviations: ABA, Abscisic Acid; ABI3, ABSCISIC ACID INSENSITIVE3; ARF, Auxin Response Factor; Aux/IAA, Auxin/ Indole-3-Acetic Acid; GA, Gibberellic Acid; ROS, Reactive Oxygen Species
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