Gibberellin 2-Oxidase Genes from Satsuma Mandarin (Citrus unshiu Marc.) Caused Late Flowering and Dwarfism in Transgenic Arabidopsis

Abstract

Gibberellins (GAs) are involved in many aspects of plant growth and development in higher plants. In this study, we aimed to characterize Satsuma mandarin (Citrus unshiu Marc.) GA 2-oxidase genes encoding enzymes with GA inactivation activity because the accumulation of active GAs is regulated by the balance between their synthesis and inactivation. We showed that CuGA2ox4, CuGA2ox2/3, and CuGA2ox8 were differentially expressed in various tissues in Satsuma mandarin and that these genes functioned like GA 2-oxidase genes in transgenic Arabidopsis. The expression pattern of CuGA2ox4 resembled that of CuGA20ox1, which was reported previously as a Satsuma mandarin GA 20-oxidase gene, in the reproductive tissues of the adult trees in that both genes were expressed in juice sacs in November and December and peel in December, suggesting that CuGA2ox4 and CuGA20ox1 act in concert to regulate the accumulation of active GAs in fruit at the maturing stage. On the other hand, CuGA2ox2/3 and CuGA2ox8 were more highly expressed in seeds and flower buds, respectively. Further study of GA biosynthetic genes, including GA 2-oxidase genes, would provide insight into the mechanism of flowering, fruit development, seedlessness, biennial bearing, and peel puffins of citrus such as Satsuma mandarin.