Rice proteome revealed antagonistic interactions between signaling components of cytokinin and ABA phytohormones during drought stress.

Cytokinins are well-known for their multifaceted roles in fine-tuning the plant growth and development during abiotic stresses in plants. An optimized concentration of cytokinins is essential to positively-influence a range of stress-dependent signaling pathways. Our study focuses on how the alteration in cytokinin levels, post CPPU (N-2-(chloro-4-pyridyl)-N-phenyl urea) application, influences the protein components of drought susceptible rice cultivar, PTT1 (Pathumthani1), under water deficit stress. The proteome was investigated by shotgun proteomics and liquid chromatography-tandem mass spectrometry (LC-MS) at tillering and grain-filling stages of rice. The results indicated that the application of CPPU had an antagonistic effect of on the biosynthesis and signaling of ABA. Drought-stressed rice plants without CPPU treatment revealed enhanced abundance of negative regulator proteins of cytokinin signaling (ORR12 and ORR21) and cytokinin dehydrogenases (CKX2 and CKX3) which are antagonistic to cytokinin responses. By contrast, CPPU treated rice plants had reduced abundance of proteins implicated in ABA biosynthesis and signaling (ZEP, NCED4, PYL9, OSK1/SnRK1A, OSK4/SnRK1B and ABIL5) but showed greater abundance proteins implicated in cytokinin signaling and responses. Further, CPPU treatment induced the abundance of some proteins implicated in maintaining the osmotic balance. The results unravel the antagonistic nature of interaction between two major phytohormones, ABA and cytokinin.