|ZHU, XUNLU - Texas Tech University|
|SUN, LI - Texas Tech University|
|KUPPU, SUNDARAM - Texas Tech University|
|HU, RONGBIN - Texas Tech University|
|MISHRA, NEELAM - Texas Tech University|
|SMITH, JENNIFER - Texas Tech University|
|ESMAEILI, NARDANA - Texas Tech University|
|HERATH, MAHSHIKA - Texas Tech University|
|GORE, MICHAEL - Cornell University|
|SHEN, GUOXIN - Zhejiang Academy Of Agricultural Sciences|
|ZHANG, HONG - Texas Tech University|
Submitted to: Nature Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2018
Publication Date: 2/7/2018
Citation: Zhu, X., Sun, L., Kuppu, S., Hu, R., Mishra, N., Smith, J., Esmaeili, N., Herath, M., Gore, M., Payton, P.R., Shen, G., Zhang, H. 2018. The yield difference between wild-type cotton and transgenic cotton that expresses IPT depends on when water-deficit stress is applied. Nature Scientific Reports. 8:2538.
Interpretive Summary: Over the past several decades, many genes have been used in efforts to genetically improve drought tolerance in plant, yet very few were successfully employed in real world conditions and today, no drought-stress specific engineered commercial products are available. The high failure rate in commercializing the genes that were promising in laboratory experiments is likely due to negative results from the field trials due to the complex nature of a multitude of stressors in production settings and disparate climate events over multiple years of field trials. We examined the effect of engineering cotton plants to express a gene involved in the biosynthesis of the plant hormone, cytokinin. Cytokinin regulates and delays plant senescence and we have shown in previous laboratory studies that altered cytokinin production results in drought stress tolerance. We conducted studys in Texas and Arizona, two significantly different production environments and found that the timing of drought stress is critical for IPT-transgenic cotton to display its yield advantage over non-transgenic control plants. When water deficit stress occured before flowering (vegetative phase), the IPT-transgenic cotton plants had higher yields compared to non-engineered plants. However, when stress was applied during flowering or fiber development, no yield advantage was detected between engineered and non-engineered plants. This result suggests that an early induction of IPT expression (before first flowering) is needed in order to realize the any yield benefits. The utilitly of IPT over-expression for stress tolerance over a wide-range of production settings needs to be tested further, but this study shows the potential for the use of this gene in semi-arid production with consistant rainfall patterns or in areas with limited irrigation where water can be saved during early season growth and used during reproductive and maturation growth phases.
Technical 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 IPTexpression in transgenic plants that face water-deficit stress later in development.