Gibberellin driven growth in elf3 mutants requires PIF4 and PIF5.
The regulatory connections between the circadian clock and hormone signaling are essential to understand, as these two regulatory processes work together to time growth processes relative to predictable environmental events. Gibberellins (GAs) are phytohormones that control many growth processes throughout all stages of the plant life cycle, including germination and flowering. An increasing number of examples demonstrate that the circadian clock directly influences GA biosynthesis and signaling. EARLY FLOWERING 3 (ELF3) participates in a tripartite transcriptional complex known as the Evening Complex (EC). In this capacity, ELF3 is fundamental to core circadian clock activity, as well as time-of-day specific regulation of genes directly responsible for growth control, namely the PHYTOCHROME INTERACTING FACTOR 4 (PIF4) and PIF5 genes. Here we show that the GA biosynthesis inhibitor paclobutrazol substantially reduces the long hypocotyl and petiole phenotypes of Arabidopsis elf3 mutants. In addition, loss of ELF3 activity causes upregulation of the key GA biosynthesis genes GA20ox1 and GA20ox2. Moreover, GA20ox1 and GA20ox2 expression depends strongly on the redundant activities of PIF4 and PIF5. These findings indicate that the defining growth phenotypes of elf3 mutants arise from altered GA biosynthesis due to misregulation of PIF4 and PIF5. These observations agree with recent work linking increased GA production with the elongated growth phenotypes of the barley elf3 mutant. Thus, the role of the EC in regulation of GA biosynthesis and signaling in eudicots is shared with monocots and, therefore, is a highly conserved mechanism for growth control.
a Keck Science Department ; Pitzer College ; Claremont , CA USA.
Julie
J
Filo
Austin
A
Wu
Erica
E
Eliason
Timothy
T
Richardson
Bryan C
BC
Thines
Frank G
FG
Harmon
D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics* / Q000378:metabolism; D057906:Circadian Clocks / Q000235:genetics*; D002940:Circadian Rhythm; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005875:Gibberellins / Q000378:metabolism*; D018546:Hypocotyl / Q000254:growth & development / Q000378:metabolism; D008027:Light; D009154:Mutation; D010641:Phenotype; D017440:Photoperiod; D063245:Plant Development / Q000235:genetics; D010937:Plant Growth Regulators / Q000378:metabolism; D018547:Plant Stems / Q000254:growth & development / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D015854:Up-Regulation
D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D005875:Gibberellins; D010937:Plant Growth Regulators; D014157:Transcription Factors; C432430:At2g25930 protein, Arabidopsis; C459466:PIF4 protein, Arabidopsis; C497729:PIF5 protein, Arabidopsis
CO, CONSTANS; Col-0, Columbia; EC, Evening Complex; ELF3, EARLY FLOWERING 3; ELF4, EARLY FLOWERING 4; EMS, ethyl methanesulfonate; FT, FLOWERING LOCUS T; GA, gibberellin; GA20ox, gibberellin 20-oxidase; GA3ox, gibberellin 3-oxidase; LD, long day; LUX, LUX ARRHYTHMO; PAC, paclobutrazol; PIF - PHYTOCHROME INTERACTING FACTOR; PIF4; SD, short day; WT, wild type; ZT, Zeitgeiber Time.; circadian clock; early flowering 3; gibberellin; phytochrome interacting factor; phytohormone; plant growth; qPCR, quantitative RT-PCR