Killing two birds with a single stone—genetic manipulation of cytokinin oxidase/dehydrogenase (CKX) genes for enhancing crop productivity and amelioration of drought stress response

Abstract

The development of high-yielding, bio-fortified, stress-tolerant crop cultivars is the need of the hour in the wake of increasing global food insecurity, abrupt climate change, and continuous shrinking of resources and landmass suitable for agriculture. The cytokinin group of phytohormones positively regulates seed yield by simultaneous regulation of source capacity (leaf senescence) and sink strength (grain number and size). Cytokinins also regulate root-shoot architecture by promoting shoot growth and inhibiting root growth. Cytokinin oxidase/dehydrogenase (CKX) are the only enzymes that catalyze the irreversible degradation of active cytokinins and thus negatively regulate the endogenous cytokinin levels. Genetic manipulation of CKX genes is the key to improve seed yield and root-shoot architecture through direct manipulation of endogenous cytokinin levels. Downregulation of CKX genes expressed in sink tissues such as inflorescence meristem and developing seeds, through reverse genetics approaches such as RNAi and CRISPR/Cas9 resulted in increased yield marked by increased number and size of grains. On the other hand, root-specific expression of CKX genes resulted in decreased endogenous cytokinin levels in roots which in turn resulted in increased root growth indicated by increased root branching, root biomass, and root-shoot biomass ratio. Enhanced root growth provided enhanced tolerance to drought stress and improved micronutrient uptake efficiency. In this review, we have emphasized the role of CKX as a genetic factor determining yield, micronutrient uptake efficiency, and response to drought stress. We have summarised the efforts made to increase crop productivity and drought stress tolerance in different crop species through genetic manipulation of CKX family genes.

Genome-Wide Identification and Abiotic-Stress-Responsive Expression of CKX Gene Family in Liriodendron chinense

“…The cytokinin group of plant hormones is involved in regulating several aspects of plant growth and development [33], many of which have direct effects on crop improvement, such as the regulation of the root crown structure [34], the regulation of inflorescence meristem tissue activity and seed yield [35,36], the regulation of leaf senescence and photosynthesis, and response to biotic and abiotic stresses [27,37,38]. According to the RNA-Seq data, under abiotic stress conditions such as drought, low-temperature treatments, and high-temperature treatments, the expression of some LcCKX genes can be changed, thus playing a defensive and protective role in plant growth and development processes, which may also be related to the resistance of goosefoot, but the exact mechanism of this effect needs to be studied in the future.…”

Heterologous expression of circular RNAs in Escherichia coli for analyzing the ligation process of chloroplastic viroids and producing double-stranded RNAs with insecticidal activity

“…In the same way, it would be interesting to exploit both versions of the system for other aspects of plant protection and improvement, such as inducing resistance to 186 viruses, abiotic stresses or increasing productivity (Tenllado et al, 2003;Vargas et al, 2008;Necira et al, 2021;Sharma et al, 2022;Ullah et al, 2022). Although the use of perfectly matched hairpins or dsRNA, both processed by the siRNA pathway, is the most common methodology for insect control, there are some examples of other RNAi pathways exploited for the same purpose (Muerdter et al, 2012;Ye et al, 2017;Bally et al, 2020;Mondal et al, 2020;Zhang et al, 2021a).…”