Effects of Soil Water Deficit on Insecticidal Protein Expression in Boll Shells of Transgenic Bt Cotton and the Mechanism

Abstract

This study was conducted to investigate the effects of soil water deficit on insecticidal protein expression in boll shells of cotton transgenic for a Bt gene. In 2014, Bt cotton cultivars Sikang 1 (a conventional cultivar) and Sikang 3 (a hybrid cultivar) were planted in pots and five soil water content treatments were imposed at peak boll stage: 15% (G1), 35% (G2), 40% (G3), 60% (G4), and 75% field capacity (CK), respectively. Four treatments (G2, G3, G4, and CK) were repeated in 2015 in the field. Results showed that the insecticidal protein content of boll shells decreased with increasing water deficit. Compared with CK, boll shell insecticidal protein content decreased significantly when soil water content was below 60% of maximum water holding capacity for Sikang 1 and Sikang 3. However, increased Bt gene expression was observed when boll shell insecticidal protein content was significantly reduced. Activity assays of key enzymes in nitrogen metabolism showed that boll shell protease and peptidase increased but nitrogen reductase and glutamic-pyruvic transaminase (GPT) decreased. Insecticidal protein content exhibited significant positive correlation with nitrogen reductase and GPT activities; and significant negative correlation with protease and peptidase activities. These findings suggest that the decrease of insecticidal protein content associated with increasing water deficit was a net result of decreased synthesis and increased decomposition.

Fitness Cost of Transgenic cry1Ab/c Rice Under Saline-Alkaline Soil Condition

“…These observations were consistent with those reported by other studies in which some insect-resistant Bt transgenic cotton lines (Zhang et al, 2017) and insect-resistant Bt transgenic corn lines (Brewer et al, 2014) under soil water stress presented significantly lower reproductive growth indices than those of the same plants grown under normal, stress-free growth conditions. On saline-alkaline and farmland soils in the absence of target insect pressure, filled grain number per plant, filled grain weight per plant and other important reproductive indices of HH1 rice were significantly lower than that of MH63 rice under the same soil conditions.…”

“…These findings were consistent with those of other studies in which some insect-resistant Bt transgenic cotton lines under salt and flooding stresses (Jiang et al, 2006; Kaur et al, 2015) and drought stress (Zhang et al, 2017), and some insect-resistant Bt transgenic corn lines under drought stress (Traore et al, 2000) had significantly lower vegetative growth ability than that of plants grown under normal, stress-free conditions. In saline-alkaline and farmland soils without target insect pressure, only the plant height of HH1 rice was significantly higher than that of MH63 rice at most growth and development stages.…”

Bt insecticidal efficacy variation and agronomic regulation in Bt cotton

“…The protein decomposition and remobilization of nitrogen also led to Bt toxin content reduction. Exposure of Bt transgenic cotton plants to high temperature resulted in a significant decline in glutamic-pyruvic transaminase (GPT) activity and soluble protein content, suggesting that high temperature may result in the degradation of soluble protein in the leaf, with a resulting decline in the level of the toxin Cry1A (Chen et al 2005), the conclusion was proved by other reports (Chen et al 2012b;Zhang et al 2017;Chen et al 2019). Pettigrew and Adamczyk (2006) reported that relocation of leaf nitrogen to boll in earlyplanted cotton resulted in decreased level of Bt protein relative to late-planted cotton plants.…”

“…The recovery was further proved that nitrogen fertilizer enhanced Bt protein expression and insect resistance (Oosterhuis and Brown 2004;Wang et al 2012;Chen et al 2018). N deficit resulted in reduced Bt protein concentration (Chen et al 2004;Zhang et al 2017). High N fertilizer rates enhanced the leaf Bt protein content by 14% compared with light nitrogen rates.…”

“…Treatment with 200 mm NaCl exhibited significant reduction of Bt protein content in the functional leaves in Bt cotton (Jiang et al 2006). Either water logging or drought significantly decreased the Bt toxin expression (Luo et al 2008;Zhang et al 2017), but the extent of reduction varied with plant organs and positions. Significant reduction of Bt protein was detected in older leaves by water deficient, but greater decrease was caused for squares by water logging (Chen et al 2012a).…”