Role and Regulation of Cytokinins in Plant Response to Drought Stress

Abstract

Cytokinins (CKs) are key phytohormones that not only regulate plant growth and development but also mediate plant tolerance to drought stress. Recent advances in genome-wide association studies coupled with in planta characterization have opened new avenues to investigate the drought-responsive expression of CK metabolic and signaling genes, as well as their functions in plant adaptation to drought. Under water deficit, CK signaling has evolved as an inter-cellular communication network which is essential to crosstalk with other types of phytohormones and their regulating pathways in mediating plant stress response. In this review, we revise the current understanding of CK involvement in drought stress tolerance. Particularly, a genetic framework for CK signaling and CK crosstalk with abscisic acid (ABA) in the precise monitoring of drought responses is proposed. In addition, the potential of endogenous CK alteration in crops towards developing drought-tolerant crops is also discussed.

From Survival to Productivity Mode: Cytokinins Allow Avoiding the Avoidance Strategy Under Stress Conditions

“…Our studies based on employing the SARK or the MT promoter fused to the IPT gene clearly demonstrated positive effect on growth and biomass production under abiotic stresses in model plants such as Arabidopsis and tobacco as well in major crops such as rice, wheat, cotton, etc. (see Gujjar and Supaibulwatana, 2019;Hai et al, 2020). Similar positive regulation of drought stress by CKs has been reported also for transgenic plants containing the SAG12 promoter fused to the IPT gene (Merewitz et al, 2010;Zhang et al, 2010).…”

“…This observation suggested that the phenomenon of CK-induced delayed senescence is also accompanied by an additional advantage of enhanced drought resistance and allowed us to suggest a novel technology for the development of drought-resistant plants ( Gepstein et al, 2017 ). Since then, major crops, including rice, wheat, peanut, cotton etc, have been developed to overexpress CKs under stress conditions (see Hai et al, 2020 ).…”

“…The role of CKs in the regulation of abiotic stress responses has been elucidated mainly during the last decade (Zwack and Rashotte, 2015;Hai et al, 2020). However, since, surprisingly, plants with exogenous CKs or biotechnological manipulation of CK endogenous levels demonstrated both positive and negative effects on the tolerance to abiotic stresses, generalizations about the effect of manipulating CK levels on overall stress tolerance are currently difficult to make (Zwack and Rashotte, 2015;Hai et al, 2020). Our studies based on employing the SARK or the MT promoter fused to the IPT gene clearly demonstrated positive effect on growth and biomass production under abiotic stresses in model plants such as Arabidopsis and tobacco as well in major crops such as rice, wheat, cotton, etc.…”

An Arabidopsis Cytokinin-Modifying Glycosyltransferase UGT76C2 Improves Drought and Salt Tolerance in Rice

“…Cytokinins (CK) are N6-substituted adenine derivatives which are originally defined as a key regulator participating in various plant developmental activities, including organ formation, apical dominance, and leaf senescence (El-Showk et al, 2013). Nowadays, increasing evidence also indicates the action of cytokinin in response to stresses (Hai et al, 2020). A recent cytokinin-responsive transcriptome analysis in rice revealed that a large number of genes are involved in both biotic and abiotic stresses (Raines et al, 2016).…”

“…Previous studies found that AHK2, AHK3, and AHK4 are negative regulators of dehydration and salt tolerance, and the ahk2 and ahk3 mutants displayed higher survival rates under severe water deprivation (Tran et al, 2007;Kang et al, 2012). However, some studies found that cytokinin could also function as a positive regulator in drought stress adaptation (Hai et al, 2020). For example, the ectopic expression of the isopentenyltransferase gene (IPT) that encodes a rate-limiting enzyme in cytokinin biosynthesis increases endogenous cytokinin levels as well as improves drought stress tolerance in transgenic cotton (Kuppu et al, 2013), creeping bentgrass (Xu et al, 2016), eggplant (Xiao et al, 2017), and tropical maize (Leta et al, 2016).…”