Plants respond and acclimatize to environmental stresses and maintain growth and productivity by modulating the expression of regulatory genes/proteins and activating the metabolism of stress-responsive signaling pathways [10,18,23]. Osmotic stresses, particularly drought and salinity which lead to reduced water content and water potential in soil, pose a global threat to agricultural productivity [11,24,34]. Water limitation under drought stress triggers a complex signaling cascade in plants due to alteration in the protein components, leading to accumulations of protective metabolites [14,19,20]. These buffered systems contribute to sustain the normal functioning of plants by avoiding the dehydration of plant tissue [19,50]. Interaction among phytohormones also plays a key role in integrating the external stress signals with internal metabolisms, thus leading to downstream stress responses [9]. Recent proteomics studies have identified several stress responsive transcription factors and developmental proteins that function together in signaling networks under drought stress [12,18]. Abscisic acid (ABA), as the central regulator of drought stress responses, influences many cellular mechanisms associated with drought resistance to reduce the water potential and dehydration of plant tissues [1,12,49]. Moderate levels of ABA signaling in plants promote beneficial physiological functions such as stomatal closure for water conservation, while high levels of ABA are more prevalent in mature tissues as an emergency signal under severe stress and are detrimental to the plant's metabolic functions leading to reduced growth and development [18,29]. Under stress environments, plants follow a survival strategy by inducing ABA biosynthesis and signaling [9]. ABA interacts with several other hormones in regulating the low water potential and drought stress responses in plants [40].

During osmotic stress conditions, cytokinin counteracts leaf senescence by redistributing the nutrients remobilized by drought stress [20,22] and improving the photosynthetic efficiency [12,45]. Further, cytokinins interrupt the drought-induced ABA responses [9,18] and eventually stop all those events that guide the plant to survive with minimal resources [4]. Cytokinins have been implicated in regulating cell division, delaying the activation of senescence pathways and mediating cellular responses to drought acclimation in agricultural crops [12,18,20,22,26]. Therefore, preventing the stress-induced decline in cytokinin signaling, and maintaining homeostasis between the concentrations of cytokinin-ABA in shoots is one of the promising ways to ameliorate the stress tolerance and improve plant's performance during stress environments [4,9,18]. Exogenous applications of synthetic cytokinins have been positively reported to influence the photosynthetic pigments, soluble sugar contents, chlorophyll stability index, leaf RWC (relative water content) and many other growth-related parameters during osmotic stresses [12,18,20,45]. Cytokinins also help in reducing the oxidative damage by increasing the activities of antioxidant enzymes [3,9]. CPPU/forchlorfenuron, a phenyl urea-based synthetic cytokinin, acts as a competitive inhibitor of cytokinin oxidase/dehydrogenase (CKX), thereby allowing the plants to retain higher cytokinin concentrations [20,31]. Further, CPPU increases the weight and size of fruit and vegetable crops [32,35] and promotes drought tolerance by enhancing chlorophyll contents, photosynthesis, soluble sugar content, and antioxidant activities under drought stress condition in agricultural crops [8,12,18,20,47]. In one of our studies, transgenic Peperomia pellucida plants overexpressing bacterial IPT (isopentenyl transferase) gene (implicated in cytokinin biosynthesis) showed increased leaf and seed size with a high percentage of fertile seeds [46]. Shotgun proteomics and liquid chromatography-tandem mass spectrometry (LC-MS) techniques are the most extensively used approaches of quantitative proteomics in recent times for investigating the whole proteome as well as differential proteome in agricultural research for dealing with biotic and abiotic stress conditions [5,[13], [15], [16], [17], [18],21]. In the present study, we report the influence of exogenous CPPU application on the abundance of functional proteins participating in the ABA biosynthesis and signaling in drought sensitive cultivar of rice. Our findings were further substantiated by STICH interaction network analysis, where we report the interaction/association of cytokinin with the proteins involved in ABA biosynthesis and signaling.