High temperature-induced abscisic acid biosynthesis and its role in the inhibition of gibberellin action in Arabidopsis seeds.
Suppression of seed germination at supraoptimal high temperature (thermoinhibiton) during summer is crucial for Arabidopsis (Arabidopsis thaliana) to establish vegetative and reproductive growth in appropriate seasons. Abscisic acid (ABA) and gibberellins (GAs) are well known to be involved in germination control, but it remains unknown how these hormone actions (metabolism and responsiveness) are altered at high temperature. Here, we show that ABA levels in imbibed seeds are elevated at high temperature and that this increase is correlated with up-regulation of the zeaxanthin epoxidase gene ABA1/ZEP and three 9-cis-epoxycarotenoid dioxygenase genes, NCED2, NCED5, and NCED9. Reverse-genetic studies show that NCED9 plays a major and NCED5 and NCED2 play relatively minor roles in high temperature-induced ABA synthesis and germination inhibition. We also show that bioactive GAs stay at low levels at high temperature, presumably through suppression of GA 20-oxidase genes, GA20ox1, GA20ox2, and GA20ox3, and GA 3-oxidase genes, GA3ox1 and GA3ox2. Thermoinhibition-tolerant germination of loss-of-function mutants of GA negative regulators, SPINDLY (SPY) and RGL2, suggests that repression of GA signaling is required for thermoinibition. Interestingly, ABA-deficient aba2-2 mutant seeds show significant expression of GA synthesis genes and repression of SPY expression even at high temperature. In addition, the thermoinhibition-resistant germination phenotype of aba2-1 seeds is suppressed by a GA biosynthesis inhibitor, paclobutrazol. We conclude that high temperature stimulates ABA synthesis and represses GA synthesis and signaling through the action of ABA in Arabidopsis seeds.
Toh
Shigeo
S
Department of Life Sciences, School of Agriculture, Meiji University, Kawasaki, Kanagawa, Japan.
Imamura
Akane
A
Watanabe
Asuka
A
Nakabayashi
Kazumi
K
Okamoto
Masanori
M
Jikumaru
Yusuke
Y
Hanada
Atsushi
A
Aso
Yukie
Y
Ishiyama
Kanako
K
Tamura
Noriko
N
Iuchi
Satoshi
S
Kobayashi
Masatomo
M
Yamaguchi
Shinjiro
S
Kamiya
Yuji
Y
Nambara
Eiji
E
Kawakami
Naoto
N
D000040:Abscisic Acid / Q000096:biosynthesis* / Q000378:metabolism; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism; D049308:Dioxygenases; D018506:Gene Expression Regulation, Plant; D005875:Gibberellins / Q000378:metabolism*; D006358:Hot Temperature; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins; D012097:Repressor Proteins / Q000378:metabolism; D012639:Seeds / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D014157:Transcription Factors / Q000378:metabolism
D029681:Arabidopsis Proteins; D005875:Gibberellins; D010940:Plant Proteins; C450823:RGL2 protein, Arabidopsis; D012097:Repressor Proteins; C101465:SPY protein, Arabidopsis; D014157:Transcription Factors; D000040:Abscisic Acid; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D010088:Oxidoreductases; C097153:zeaxanthin epoxidase; D010105:Oxygenases; D049308:Dioxygenases; C109043:9-cis-epoxy-carotenoid dioxygenase; C089210:gibberellin, 2-oxoglutarate-oxygen oxidoreductase (20-hydroxylating, oxidizing); C108186:gibberellin 3beta-hydroxylase