14-3-3 adaptor proteins are intermediates in ABA signal transduction during barley seed germination.
Proteins of the 14-3-3 family have well-defined functions as regulators of plant primary metabolism and ion homeostasis. However, neither their function nor action mechanism in plant hormonal signaling have been fully addressed. Here we show that abscisic acid (ABA) affects both expression and protein levels of five 14-3-3 isoforms in embryonic barley roots. As ABA prolongs the presence of 14-3-3 proteins in the elongating radicle, we tested whether 14-3-3s are instrumental in ABA action using RNA interference. Transient co-expression of 14-3-3 RNAi constructs along with an ABA-responsive promoter showed that each 14-3-3 is functional in generating an ABA response. In a yeast two-hybrid screen, we identified three new 14-3-3 interactors that belong to the ABF protein family. Moreover, using a yeast two-hybrid assay, we show that the transcription factor HvABI5, which binds to cis-acting elements of the ABA-inducible HVA1 promoter, interacts with three of the five 14-3-3s. Our analyses identify two 14-3-3 binding motifs in HvABI5 that are essential for 14-3-3 binding and proper in vivo trans-activation activity of HvABI5. In line with these results, 14-3-3 silencing effectively blocks trans-activation. Our results indicate that 14-3-3 genes/proteins are not only under the control of ABA, but that they control ABA action as well.
Schoonheim
Peter J
PJ
Department of Structural Biology, Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands.
Sinnige
Mark P
MP
Casaretto
Jose A
JA
Veiga
Helena
H
Bunney
Tom D
TD
Quatrano
Ralph S
RS
de Boer
Albertus H
AH
D048948:14-3-3 Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D000040:Abscisic Acid / Q000494:pharmacology*; D000595:Amino Acid Sequence; D001665:Binding Sites; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D018525:Germination / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D005966:Glucuronidase / Q000235:genetics / Q000378:metabolism; D001467:Hordeum / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D016415:Sequence Alignment; D015398:Signal Transduction; D020798:Two-Hybrid System Techniques
D048948:14-3-3 Proteins; D010940:Plant Proteins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D000040:Abscisic Acid; D005966:Glucuronidase