Abstract
To explore the stability of insect resistance during the development of transgenic insect-resistant trees, this study investigated how insect resistance changes as transgenic trees age. We selected 19 transgenic insect-resistant triploid Populus tomentosa lines as plant material. The presence of exogenous genes and Cry1Ac protein expression were verified using polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) analyses. The toxicity for Clostera anachoreta and Lymantria dispar was evaluated by feeding fresh leaves to first instar larvae after the trees were planted in the field for 2 years and after the sixth year. Results of PCR showed that the exogenous genes had a long-term presence in the poplar genome. ELISA analyses showed significant differences existed on the 6-year-old transgenic lines. The insect-feeding experiment demonstrated significant differences in the mortality rates of C. anachoreta and L. dispar among different transgenic lines. The average corrected mortality rates of C. anachoreta and L. dispar ranged from 5.6–98.7% to 35.4–7.2% respectively. The larval mortality rates differed significantly between the lines at different ages. Up to 52.6% of 1-year-old transgenic lines and 42.1% of 2-year-old transgenic lines caused C. anachoreta larval mortality rates to exceed 80%, whereas only 26.3% of the 6-year-old transgenic lines. The mortality rates of L. dispar exhibited the same trend: 89.5% of 1-year-old transgenic lines and 84.2% of 2-year-old transgenic lines caused L. dispar larval mortality rates to exceed 80%; this number decreased to 63.2% for the 6-year-old plants. The proportion of 6-year-old trees with over 80% larval mortality rates was clearly lower than that of the younger trees. The death distribution of C. anachoreta in different developmental stages also showed the larvae that fed on the leaves of 1-year-old trees were killed mostly during L1 and L2 stages, whereas the proportion of larvae that died in L3 and L4 stages was significantly increased when fed on leaves of 6-year-old trees. Results of correlation analysis showed there was a significant correlation between the larvae mortality rates of trees at different ages, as well as between Cry1Ac protein contents and larvae mortality rates of 6-year-old trees.
Highlights
Poplars are trees commonly used in afforestation programs and are widely planted throughout most of China for various purposes
We studied the insect resistance changes of different lines transformed with Bt gene and API gene in different developmental stages to explore the exogenous gene expression differences and stability in adult transgenic poplar trees
To determine the differential expression and stability of the exogenous genes in mature transgenic poplar trees, we studied the transgenic P. tomentosa lines with the exogenous genes at different developmental stages in terms of toxin gene stability and insect resistance
Summary
Poplars are trees commonly used in afforestation programs and are widely planted throughout most of China for various purposes. Some selected lines showed high resistance to C. anachoreta, L. dispar, H. cunea, and other lepidopterans (Tian et al, 2000) This poplar was authorized for commercial production in 2002 (Lu and Hu, 2006). Few studies focused on different transgenic lines and how their insect resistance changed as the trees aged. We studied the insect resistance changes of different lines transformed with Bt gene and API gene in different developmental stages to explore the exogenous gene expression differences and stability in adult transgenic poplar trees. Data from this study are essential to determine which changes in trees are caused by field conditions and to provide a basis for the selection of clones with high and stable insect resistance
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