Cytokinin antagonizes abscisic acid-mediated inhibition of cotyledon greening by promoting the degradation of abscisic acid insensitive5 protein in Arabidopsis.
In higher plants, seed germination is followed by postgerminative growth. One of the key developmental events during postgerminative growth is cotyledon greening, which enables a seedling to establish photosynthetic capacity. The plant phytohormone abscisic acid (ABA) plays a vital role by inhibiting seed germination and postgerminative growth in response to dynamically changing internal and environmental cues. It has been shown that abscisic acid insensitive5 (ABI5), a basic leucine zipper transcription factor, is an important factor in the regulation of the ABA-mediated inhibitory effect on seed germination and postgerminative growth. Conversely, the phytohormone cytokinin has been proposed to promote seed germination by antagonizing the ABA-mediated inhibitory effect. However, the underpinning molecular mechanism of cytokinin-repressed ABA signaling is largely unknown. Here, we show that cytokinin specifically antagonizes ABA-mediated inhibition of 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 cytokinin response1/Arabidopsis histidine kinase4, downstream histidine phosphotransfer protein genes AHP2, AHP3, and AHP5, 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 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 of postgerminative growth.
State Key Laboratory of Plant Genomics and National Plant Gene Research Center, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
Chunmei
C
Guan
Xingchun
X
Wang
Jian
J
Feng
Sulei
S
Hong
Yan
Y
Liang
Bo
B
Ren
Jianru
J
Zuo
D000040:Abscisic Acid / Q000494:pharmacology*; D017360:Arabidopsis / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D050976:Basic-Leucine Zipper Transcription Factors / Q000378:metabolism*; D018548:Cotyledon / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D003583:Cytokinins; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D059748:Proteolysis / Q000187:drug effects*; D015398:Signal Transduction / Q000187:drug effects; D014157:Transcription Factors / Q000378:metabolism
C409743:ABI5 protein, Arabidopsis; C519632:ARR12 protein, Arabidopsis; D029681:Arabidopsis Proteins; D050976:Basic-Leucine Zipper Transcription Factors; D003583:Cytokinins; D014157:Transcription Factors; D000040:Abscisic Acid; D046988:Proteasome Endopeptidase Complex