Performance and Nutritional Assessment of Transgenic Tropical Maize (Zea Mays L.) Harbouring Isopentenyl Transferase Gene Under Drought Stress

Abstract

Maize productivity is significantly influenced by various abiotic factors key among them drought. Development of crops that are tolerant to drought via genetic engineering is considered the best possible solution to this problem. However, how these genes are inherited as well as whether the traits persist in successive generations of selfing is not yet known. Additionally, the nutritional profile of this transgenic maize has not been characterized. This study sought to use farmer-preferred maize line (CML-144) transgenic maize previously transformed with isopentenyl transferase (IPT) gene under the regulation of Senescence-Associated Receptor Kinase (SARK) promoter to confer drought tolerance. The objective of the study was to evaluate the agronomic performance and nutritional composition of the pSARK::IPT transgenic maize under drought conditions towards possible advancement to contained and confined field trials. The transgenic maize seeds harboring pSARK::IPT and its non-transgenic control were planted in potted soil. Germinated plants (T3) were screened to determine presence of transgene via polymerase chain reaction (PCR). Selfing was done to generate T4 plants, which were also screened for presence of transgene. PCR-positive plants in T4 generation were selected for drought assay. Fifteen transgenic and 15 non-transgenic controls at eight weeks were exposed to drought stress for three weeks by withholding water then re-watered to maturity. Data on growth of stressed and unstressed plants were collected and analyzed using student’s t-test at 95% confidence interval in GraphPad Prism statistical software version 8.4.3.683, followed by correlation analysis. The current study reported that pSARK::IPT transformed plants contained the transfer DNA (T-DNA) in T3 and T4 generations. Out of 125 transgenic events screened via PCR, only 45 were positive for the transgene. T4 generation plants exhibited significantly higher relative water content, higher chlorophyll amounts, and elevated antioxidant enzyme activities as well as delayed senescence compared to the non-transformed plants under drought stress. However, there were no significant differences in yield between the transgenic and non-transgenic maize plants under drought stress. Notably, the well-watered transgenic plants had 45% higher more kernels per ear than their non-transgenic counterparts. Moreover, pSARK::IPT maize kernels had 47% and 7.5% higher crude protein and fat content respectively than their non-transgenic control. The study confirms presence of the pSARK::IPT transgene, a key phenomenon for successful transformation. The pSARK::IPT enhances yield even in well-watered conditions was higher. This study recommends further evaluation of these genotypes for their stability over time so that the transgenic plants can be considered for field trials in ecoregions with unreliable rainfall.