Transcriptome-Based Construction of the Gibberellin Metabolism and Signaling Pathways in Eucalyptus grandis × E. urophylla, and Functional Characterization of GA20ox and GA2ox in Regulating Plant Development and Abiotic Stress Adaptations

Abstract

Gibberellins (GAs) are the key regulators controlling plant growth, wood production and the stress responses in perennial woody plants. The role of GA in regulating the above-mentioned processes in <i>Eucalyptus</i> remain largely unclear. There is still a lack of systematic identification and functional characterization of GA-related genes in <i>Eucalyptus</i>. In this study, a total of 59,948 expressed genes were identified from the major vegetative tissues of the <i>E. grandis</i> × <i>E. urophylla</i> using transcriptome sequencing. Then, the key gene families in each step of GA biosynthesis, degradation and signaling were investigated and compared with those of <i>Arabidopsis</i>, rice, and <i>Populus</i>. The expression profile generated using Real-time quantitative PCR showed that most of these genes exhibited diverse expression patterns in different vegetative organs and in response to abiotic stresses. Furthermore, we selectively overexpressed <i>EguGA20ox1</i>, <i>EguGA20ox2</i> and <i>EguGA2ox1</i> in both <i>Arabidopsis</i> and <i>Eucalyptus</i> via <i>Agrobacterium tumefaciens</i> or <i>A. rhizogenes</i>-mediated transformation. Though both <i>Arabidopsis EguGA20ox1</i>- and <i>EguGA20ox2</i>-overexpressing (OE) lines exhibited better vegetative growth performance, they were more sensitive to abiotic stress, unlike <i>EguGA2ox1</i>-OE plants, which exhibited enhanced stress resistance. Moreover, overexpression of <i>EguGA20ox</i> in <i>Eucalyptus</i> roots caused significantly accelerated hairy root initiation and elongation and improved root xylem differentiation. Our study provided a comprehensive and systematic study of the genes of the GA metabolism and signaling and identified the role of <i>GA20ox</i> and <i>GA2ox</i> in regulating plant growth, stress tolerance, and xylem development in <i>Eucalyptus</i>; this could benefit molecular breeding for obtaining high-yield and stress-resistant <i>Eucalyptus</i> cultivars.