Cytokinin antagonizes abscisic acid-mediated inhibition of cotyledon greening by promoting the degradation of ABI5 protein in Arabidopsis
| 作者： |
Chunmei Guan,Xingchun Wang,Jian Feng,Sulei Hong,Yan Liang,Bo Ren,and Jianru Zuo |
| 刊物名称： |
Plant Physiol |
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| 发表年度： |
2014-01-18 |
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| 摘要： |
In higher plants, seed germination is followed by postgerminative growth. One of the key developmental events during postgerminative growth is cotyledon greening that enables a seedling establish the photosynthetic capacity. The plant phytohormone abscisic acid (ABA) plays a vital role by inhibiting seed germination and postgerminative growth in response to the dynamically changing internal and environmental cues. It has been shown that ABSCISIC ACID INSENSITIVE 5 (ABI5), a bZIP transcription factor, is an important factor in the regulation of ABA-mediated inhibitory effect on seed germination and postgerminative growth. Conversely, the phytohormone cytokinin has been proposed to promote seed germination by antagonizing ABA-mediated inhibitory effect. However, the underpinning molecular mechanism of the cytokinin-repressed ABA signaling is largely unknown. Here, we show that cytokinin specifically antagonizes ABA-mediated inhibition on cotyledon greening with minimal effects on seed germination in Arabidopsis (Arabidopsis thaliana). We found that the cytokinin-antagonized ABA effect is dependent on a functional cytokinin signaling pathway, mainly involved in the cytokinin receptor gene CRE1/AHK4, downstream AHP2, 3, 5 genes, and a type-B response regulator gene ARR12, which genetically acts upstream of ABI5 to regulate cotyledon greening. Cytokinin has no apparent effect on the transcription of ABI5. However, cytokinin efficiently promotes the proteasomal degradation of ABI5 protein in a cytokinin signaling-dependent manner. These results define a genetic pathway, through which cytokinin specifically induces the degradation of ABI5 protein, thereby antagonizing ABA-mediated inhibition on postgerminative growth. |
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