A new role for the Arabidopsis AP2 transcription factor, LEAFY PETIOLE, in gibberellin-induced germination is revealed by the misexpression of a homologous gene, SOB2/DRN-LIKE.
Gibberellic acid (GA) promotes germination, stem/hypocotyl elongation, and leaf expansion during seedling development. Using activation-tagging mutagenesis, we identified a mutation, sob2-D (for suppressor of phytochromeB-4 [phyB-4]#2 dominant), which suppresses the long-hypocotyl phenotype of a phyB missense allele, phyB-4. This mutant phenotype is caused by the overexpression of an APETALA2 transcription factor, SOB2, also called DRN-like. SOB2/DRN-like transcript is not detectable in wild-type seedling or adult tissues via RT-PCR analysis, suggesting that SOB2/DRN-like may not be involved in seedling development under normal conditions. Adult sob2-D phyB-4 plants have curled leaves and club-like siliques, resembling plants that overexpress a closely related gene, LEAFY PETIOLE (LEP). Hypocotyls of a LEP-null allele, lep-1, are shorter in the light and dark, suggesting LEP involvement in seedling development. This aberrant hypocotyl phenotype is due at least in part to a delay in germination. In addition, lep-1 is less responsive to GA and more sensitive to the GA biosynthesis inhibitor paclobutrazol, indicating that LEP is a positive regulator of GA-induced germination. RT-PCR shows that LEP transcript accumulates in wild-type seeds during imbibition and germination, and the transcript levels of REPRESSOR OF ga1-3-LIKE2 (RGL2), a negative regulator of GA signaling during germination, is unaffected in lep-1. These results suggest LEP is a positive regulator of GA-induced germination acting independently of RGL2. An alternative model places LEP downstream of RGL2 in the GA-signaling cascade.
Ward
Jason M
JM
Department of Biology, Washington University, St. Louis, Missouri 63130, USA.
Smith
Alison M
AM
Shah
Purvi K
PK
Galanti
Sarah E
SE
Yi
Hankuil
H
Demianski
Agnes J
AJ
van der Graaff
Eric
E
Keller
Beat
B
Neff
Michael M
MM
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000033:anatomy & histology / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D003624:Darkness; D018506:Gene Expression Regulation, Plant; D018525:Germination / Q000187:drug effects* / Q000502:physiology; D005875:Gibberellins / Q000494:pharmacology*; D008027:Light; D008969:Molecular Sequence Data; D009154:Mutation; D016376:Oligonucleotides, Antisense; D010641:Phenotype; D010937:Plant Growth Regulators / Q000494:pharmacology*; D036226:Seedlings / Q000033:anatomy & histology / Q000502:physiology; D012639:Seeds / Q000502:physiology; D016415:Sequence Alignment; D015398:Signal Transduction / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D029681:Arabidopsis Proteins; D005875:Gibberellins; C480525:LEP protein, Arabidopsis; D016376:Oligonucleotides, Antisense; D010937:Plant Growth Regulators; C450823:RGL2 protein, Arabidopsis; D014157:Transcription Factors