Abstract
A microarray developed on the basis of 2895 unique transcripts from larval gut was used to compare gut gene expression profiles between a laboratory-selected Cry1Ab-resistant (R) strain and its isoline susceptible (S) strain of the European corn borer (Ostrinia nubilalis) after the larvae were fed the leaves of transgenic corn (MON810) expressing Cry1Ab or its non-transgenic isoline for 6 h. We revealed 398 gut genes differentially expressed (i.e., either up- or down-regulated genes with expression ratio ≥2.0) in S-strain, but only 264 gut genes differentially expressed in R-strain after being fed transgenic corn leaves. Although the percentages of down-regulated genes among the total number of differentially expressed genes (50% in S-strain and 45% in R-strain) were similar between the R- and S-strains, the expression ratios of down-regulated genes were much higher in S-strain than in R-strain. We revealed that 17 and 9 significantly up- or down-regulated gut genes from S and R-strain, respectively, including serine proteases and aminopeptidases. These genes may be associated with Cry1Ab toxicity by degradation, binding, and cellular defense. Overall, our study suggests enhanced adaptation of Cry1Ab-resistant larvae on transgenic Cry1Ab corn as revealed by lower number and lower ratios of differentially expressed genes in R-strain than in S-strain of O. nubilalis.
Highlights
Transgenic crops expressing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) have been adopted in insect pest management programs worldwide [1]
A Dipel-selected strain of O. nubilalis was found to be associated with reduced protease activity and its resistance can be virtually abolished when resistant insects were fed on transgenic Bt corn (MON810-event) [6,10]
This suggests that these 48 genes may be directly or indirectly involved in cell protection during Cry1Ab attack (Table S2). Several genes, such as contig[0814], contig[0009], and contig[4527], were down-regulated in all the three treatments, and the highest down-regulation ratios were found in S-strain larvae fed transgenic corn leaves, whereas the lowest down-regulation ratios existed in R-strain larvae fed transgenic corn leaves. These results suggested that the change of gut gene expression in R-strain larvae was less responsive to the ingestion of transgenic corn expressing Cry1Ab toxin than that of S-strain larvae, which could be explained by the adaptation of R strain larvae to Cry1Ab toxin
Summary
Transgenic crops expressing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) have been adopted in insect pest management programs worldwide [1]. A Dipel-selected strain of O. nubilalis was found to be associated with reduced protease activity and its resistance can be virtually abolished when resistant insects were fed on transgenic Bt corn (MON810-event) [6,10]. A highly variable Cad protein (caused by alternative splicing) was found to associate with field-evolved resistance to Bt cotton in P. gossypiella [12], and a deletion mutation in the aminopeptidase N1 gene was related to Cry1Ac resistance in H. arimgera [13]. The mitogen-activated protein kinase pathway (MARK signaling pathway) appeared to alter the expression of ALP and ATP-binding cassette transporter subfamily C (ABCC) genes in the gut of a Cry1Ac resistant strain of Plutella xylostella [17]
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