Abstract
Although Catalpa bungei is a forest plant with considerable economic and ornamental value in China, its wood and decorative qualities are constrained by insect pests such as the shoot borer Omphisa plagialis (Lepidoptera). Overexpressing insect resistance genes such as crystal genes to develop an insect-resistant variety of C. bungei is an environmental and ecological approach. However, genotype limitations and low regeneration rates of embryogenic calli (EC) inhibit the development of transformation and the insect-resistant gene expression system in C. bungei. Here, we first established embryogenic callus induction and regeneration systems of five genotypes using mature seed and stem segment explants; the highest induction and regeneration rates of EC were 39.89 and 100%, respectively. Next, an efficient and stable Agrobacterium-mediated genetic transformation system was developed from EC and its positive frequency was up to 92.31%. Finally, using the transformation system, 15 and 22 transgenic C. bungei lines that expressed Cry2A and Cry9Aa-like were generated, respectively. These transgenic lines that exhibited significantly higher resistance to O. plagialis in the laboratory and field have great promise for meeting the challenge of future pest management under changing climatic conditions. Additionally, this efficient, fast, and stable transformation system could be a potential tool for gene function analysis and forest tree genetic improvement.
Highlights
Catalpa bungei is both an economically important tree with high-quality wood and a magnificent ornamental tree because it is tall with a straight tree trunk and attractive and elegant flowers
As the sucrose concentration increased, the degree of callus browning gradually deepened (Supplementary Figure 2). These calli were transferred to ECMs and the statistics showed that ECM16 was the most suitable medium for embryogenic calli (EC) induction because approximately 10.61% of brown calli induced EC (Figure 1D and Supplementary Table 2)
The EC transferred to ECMs with Murashige and Skoog (MS) basal medium were highly proliferative, especially ECM4 (2–3 times the initial amount after 20 days) (Figure 1I)
Summary
Catalpa bungei is both an economically important tree with high-quality wood and a magnificent ornamental tree because it is tall with a straight tree trunk and attractive and elegant flowers O. plagialis can invade C. bungei young shoots from the base of the petiole into the pith of the shoots to form galls, which causes them to wither or die (Hong et al, 2016; Supplementary Figure 1). This pest is responsible for losses of up to 80% if no control measures
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