The yield difference between wild-type cotton and transgenic cotton that expresses IPT depends on when water-deficit stress is applied

Xunlu Zhu,Guoxin Shen,Sundaram Kuppu,Li Sun,Michael A Gore,Neelam Mishra,Nardana Esmaeili,Hong Zhang,Paxton Payton,Maheshika Herath,Rongbin Hu,Jennifer Smith

doi:10.1038/s41598-018-20944-7

Abstract

Drought is the No. 1 factor that limits agricultural production in the world, thus, making crops more drought tolerant is a major goal in agriculture. Many genes with functions in abiotic stress tolerance were identified, and overexpression of these genes confers increased drought tolerance in transgenic plants. The isopentenyltransferase gene (IPT) that encodes a rate limiting enzyme in cytokinin biosynthesis is one of them. Interestingly, when IPT-transgenic cotton was field-tested at two different sites, Texas and Arizona, different results were obtained. To explain this phenomenon, reduced irrigation experiments with different timing in applying water deficit stress were conducted. It was found that the timing of water deficit stress is critical for IPT-transgenic cotton to display its yield advantage over control plants (i.e. wild-type and segregated non-transgenic plants). If water deficit stress occurs before flowering (vegetative phase), IPT-transgenic cotton would outperform control plants; however, if water deficit stress occurs at or after flowering (reproductive phase), there would not be a yield difference between IPT-transgenic and control cotton plants. This result suggests that an early induction of IPT expression (before first flowering) is needed in order to realize the benefits of IPT-expression in transgenic plants that face water-deficit stress later in development.

Highlights

Fresh water shortage is the most critical factor that limits agricultural production, and affects the stability of many countries
In Texas, we found that isopentenyltransferase gene (IPT)-transgenic cotton lines outperformed control plants under dryland conditions in 2010 and 2011 (Figs 1 and 2)
To explain the reason for obtaining different results in Arizona, we designed new experiments to test our hypothesis that the timing of water deficit stress is critical for IPT-transgenic cotton lines to show its advantage over control lines

Summary

Introduction

Fresh water shortage is the most critical factor that limits agricultural production, and affects the stability of many countries. A group of genes in the families of DREBs or NACs encoding transcriptional factors that bind to the promoters of the downstream genes, are water deficit induced, thereby, activating downstream gene expression and enabling plants to acquire increased drought tolerance[7,8] Another group of genes that showed great potential are the ones encoding functional enzymes or membrane-bound transporter proteins. Many genes hold great promise in increasing drought tolerance in laboratory and greenhouse studies, so far very few have been commercialized, except in one case where Monsanto appeared to have released a drought tolerant maize line[15] This maize line expresses a bacterial cold shock protein that aids in withholding water under drought conditions. Based on the limited information about this line, it can be assumed that unless the margin of the yield advantage is larger than 5–10% under drought conditions, it may be difficult to convince farmers to adopt this line for large scale cultivation, as they are required to pay a higher price to buy the transgenic seeds

Methods

Results

Conclusion