Differential expression and affinities of Arabidopsis gibberellin receptors can explain variation in phenotypes of multiple knock-out mutants.
In Arabidopsis, three receptors exist for the phytohormone gibberellin. Of the three, only a double loss-of-function mutant (atgid1a atgid1c) shows a dwarf phenotype, while other double and all single mutants show no abnormality in height. In this study we show that the expression of AtGID1b-GUS mRNA, driven by the AtGID1b promoter, is low in inflorescence stems, but may be 10% of AtGID1a-GUS mRNA, driven by the AtGID1a promoter. However, AtGID1b-GUS enzymatic activity does not exist in them. This factor strongly suggests that atgid1a atgid1c lacks sufficient AtGID1b protein for normal stem growth. In the stamens of pAtGID1c::AtGID1c-GUS transformants, we detected clear AtGID1c-GUS activity, while another atgid1a atgid1b, which has short stamens in its flowers, causes the adhesion of little pollen to stigmas thus leading to its low fertility. We then evaluated the affinity of the AtGID1-DELLA interaction by a competitive yeast three-hybrid system and also by QCM apparatus. AtGID1c showed a quite lower affinity to RGL2, the major DELLA protein in floral buds, than AtGID1a or AtGID1b. The low affinity of the AtGID1c-RGL2 interaction is likely to be responsible for the failure of AtGID1c to hold RGL2, which is required for normal stamen development. Taken together with expressional information of DELLA genes, we propose that in a double loss-of-function mutant of gibberellin receptors, the emergence of any phenotype(s) depends on the abundance of the remaining receptor and its preference to DELLA proteins existing at a target site.
Suzuki
Hiroyuki
H
Department of Applied Biological Chemistry, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.
Park
Seung-Hyun
SH
Okubo
Kyoko
K
Kitamura
Jun
J
Ueguchi-Tanaka
Miyako
M
Iuchi
Satoshi
S
Katoh
Etsuko
E
Kobayashi
Masatomo
M
Yamaguchi
Isomaro
I
Matsuoka
Makoto
M
Asami
Tadao
T
Nakajima
Masatoshi
M
D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D005875:Gibberellins / Q000378:metabolism*; D009154:Mutation; D010641:Phenotype; D010937:Plant Growth Regulators / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000254:growth & development; D011485:Protein Binding; D018749:RNA, Plant / Q000235:genetics; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
D029681:Arabidopsis Proteins; C512225:GID1a protein, Arabidopsis; C512226:GID1b protein, Arabidopsis; C512227:GID1c protein, Arabidopsis; D005875:Gibberellins; D010937:Plant Growth Regulators; D018749:RNA, Plant; D011956:Receptors, Cell Surface