Overexpression of Jatropha Gibberellin 2-oxidase 6 (JcGA2ox6) Induces Dwarfism and Smaller Leaves, Flowers and Fruits in Arabidopsis and Jatropha.

Ying-Xiong Hu,Yan-Bin Tao,Zeng-Fu Xu

doi:10.3389/fpls.2017.02103

Abstract

Gibberellins (GAs) are plant hormones that play fundamental roles in plant growth and development. Gibberellin 2-oxidase (GA2ox) plays a direct role in determining the levels of bioactive GAs by catalyzing bioactive GAs or their immediate precursors to inactive forms. In this study, a GA2ox gene, designated JcGA2ox6, was isolated from Jatropha curcas. JcGA2ox6 is expressed in all tissues of adult Jatropha, with the highest expression level in male flowers and the lowest expression level in young leaves. Overexpression of JcGA2ox6 in Arabidopsis resulted in a typical dwarf phenotype, along with late flowering, smaller leaves and flowers, shorter siliques and smaller seeds. Similarly, when JcGA2ox6 was overexpressed in Jatropha, the transgenic plants exhibited a dwarf phenotype with dark-green leaves and smaller inflorescences, flowers, fruits and seeds. However, the flowering time of Jatropha was not affected by overexpression of JcGA2ox6, unlike that in the transgenic Arabidopsis. Moreover, the number of flowers per inflorescence, the weight of 10 seeds and the seed oil content were significantly decreased in transgenic Jatropha. The results indicated that overexpression of JcGA2ox6 had a great impact on the vegetative and reproductive growth of transgenic Jatropha. Furthermore, we found that the dwarf phenotype of transgenic Jatropha was caused by a decrease in endogenous bioactive GA4, which was correlated with the degree of dwarfism.

Highlights

Physic nut (Jatropha curcas L.) is a perennial woody plant that belongs to the Euphorbiaceae family and is monoecious, with male and female flowers borne on the same inflorescence (Divakara et al, 2010)
The analysis showed that JcGA2ox2, JcGA2ox4, and JcGA2ox6 have the highest identity with RcGA2ox2, RcGA2ox4, and RcGA2ox5 protein from Ricinus communis, respectively, and that they clustered with the C19GA2ox group of Arabidopsis
The transgenic Arabidopsis and Jatropha overexpressing JcGA2ox6 demonstrated the GA-deficient phenotype of dwarfism

Summary

Introduction

Physic nut (Jatropha curcas L.) is a perennial woody plant that belongs to the Euphorbiaceae family and is monoecious, with male and female flowers borne on the same inflorescence (Divakara et al, 2010). The Function of Jatropha Gibberellin 2-oxidase 6 Gene in Jatropha promoted the transition of shoot growth from the vegetative to reproductive phase, which resulted in significant increases in the numbers of inflorescence and infructescence per plant and, a higher seed yield (Ghosh et al, 2010; Song et al, 2013). Reduced levels of endogenous GA have been correlated with flowering in citrus (Koshita et al, 1999) and lychee plants (Chen, 1990) These studies suggest that GA suppresses floral initiation in perennial woody plants, which is contrary to the role of GA in promoting flowering in most herbaceous plants such as Arabidopsis (Blazquez et al, 1998), maize (Evans and Poethig, 1995), and chrysanthemums (Dong et al, 2017).

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