SOMNUS, a CCCH-type zinc finger protein in Arabidopsis, negatively regulates light-dependent seed germination downstream of PIL5.
Light absorbed by seed phytochromes of Arabidopsis thaliana modulates abscisic acid (ABA) and gibberellic acid (GA) signaling pathways at least partly via PHYTOCHROME-INTERACTING FACTOR3-LIKE5 (PIL5), a phytochrome-interacting basic helix-loop-helix transcription factor. Here, we report a new mutant, somnus (som), that germinates in darkness, independently of various light regimens. SOM encodes a nucleus-localized CCCH-type zinc finger protein. The som mutant has lower levels of ABA and elevated levels of GA due to expressional changes in ABA and GA metabolic genes. Unlike PIL5, however, SOM does not regulate the expression of GA-INSENSITIVE and REPRESSOR OF GA1 (RGA/RGA1), two DELLA genes encoding GA negative signaling components. Our in vivo analysis shows that PIL5 activates the expression of SOM by binding directly to its promoter, suggesting that PIL5 regulates ABA and GA metabolic genes partly through SOM. In agreement with these results, we also observed that the reduced germination frequency of a PIL5 overexpression line is rescued by the som mutation and that this rescue is accompanied by expressional changes in ABA and GA metabolic genes. Taken together, our results indicate that SOM is a component in the phytochrome signal transduction pathway that regulates hormone metabolic genes downstream of PIL5 during seed germination.
Kim
Dong Hwan
DH
Department of Biological Sciences, KAIST, Daejeon 305-701, Korea.
Yamaguchi
Shinjiro
S
Lim
Soohwan
S
Oh
Eunkyoo
E
Park
Jeongmu
J
Hanada
Atsushi
A
Kamiya
Yuji
Y
Choi
Giltsu
G
D000040:Abscisic Acid / Q000378:metabolism; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D047369:Chromatin Immunoprecipitation; D024202:Electrophoretic Mobility Shift Assay; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D018525:Germination / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D005875:Gibberellins / Q000378:metabolism; D008027:Light; D008969:Molecular Sequence Data; D010834:Phytochrome / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012639:Seeds / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D016335:Zinc Fingers / Q000235:genetics
D000040:Abscisic Acid; D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D002352:Carrier Proteins; D005875:Gibberellins; D010834:Phytochrome; C533360:SOMNUS protein, Arabidopsis; C007842:gibberellic acid; C508068:At2g20180 protein, Arabidopsis