Differential Regulation of RNA Levels of Gibberellin Dioxygenases by Photoperiod in Spinach

Abstract

Abstract Previous work with spinach (Spinacia oleracea) has shown that the level of gibberellin (GA) 20-oxidase is strongly up-regulated by long days (LD). In the present work, the effect of photoperiod on expression of other GA dioxygenases was investigated and compared with that of GA 20-oxidase. Two GA 2-oxidases and one GA 3-oxidase were isolated from spinach by reverse transcription-polymerase chain reaction with degenerate primers and by 5′- and 3′-rapid amplification of cDNA ends. As determined by high-performance liquid chromatography with on-line radioactivity detection, the SoGA3ox1 gene product catalyzed 3β-hydroxylation of GA9 to GA4 and GA20 to GA1. The SoGA2ox1 and the SoGA2ox2 gene products catalyzed 2β-hydroxylation of GA9 to GA51 and GA20 to GA29. The product of GA20 metabolism by SoGA3ox1 was identified as GA1 by gas chromatography-mass spectrometry, whereas the products of GA1 and GA20 metabolism by SoGA2ox1 and SoGA2ox2 were identified as GA8 and GA29, respectively. SoGA2ox1 also metabolized GA53 to GA97. The levels ofSoGA20ox1 transcripts were greatly increased in all organs tested in LD conditions, but the levels ofSoGA3ox1 transcripts were only slightly increased in blades and petioles. A decrease in the levels of theSoGA2ox1 transcripts in young leaves and tips in LD conditions is opposite to the expression pattern of theSoGA20ox1. Expression of SoGA20ox1 in petioles and young leaves was strongly up-regulated by a supplementary 16 h of light, but the levels of SoGA3ox1 andSoGA2ox1 transcripts did not change. It is concluded that regulation and maintenance of GA1 concentration in spinach are primarily attributable to changes in expression ofSoGA20ox1.