Abstract
Comparative characterization of microRNA-mediated stress regulatory networks in contrasting rice cultivars is critical to decipher plant stress response. Consequently, a multi-level comparative analysis, using sRNA sequencing, degradome analysis, enzymatic and metabolite assays and metal ion analysis, in drought tolerant and sensitive rice cultivars was conducted. The study identified a group of miRNAs “Cultivar-specific drought responsive” (CSDR)-miRNAs (osa-miR159f, osa-miR1871, osa-miR398b, osa-miR408-3p, osa-miR2878-5p, osa-miR528-5p and osa-miR397a) that were up-regulated in the flag-leaves of tolerant cultivar, Nagina 22 (N22) and Vandana, but down-regulated in the sensitive cultivar, Pusa Basmati 1 (PB1) and IR64, during drought. Interestingly, CSDR-miRNAs target several copper-protein coding transcripts like plantacyanins, laccases and Copper/Zinc superoxide dismutases (Cu/Zn SODs) and are themselves found to be similarly induced under simulated copper-starvation in both N22 and PB1. Transcription factor OsSPL9, implicated in Cu-homeostasis also interacted with osa-miR408-3p and osa-miR528-5p promoters. Further, N22 flag leaves showed lower SOD activity, accumulated ROS and had a higher stomata closure. Interestingly, compared to PB1, internal Cu levels significantly decreased in the N22 flag-leaves, during drought. Thus, the study identifies the unique drought mediated dynamism and interplay of Cu and ROS homeostasis, in the flag leaves of drought tolerant rice, wherein CSDR-miRNAs play a pivotal role.
Highlights
Rice production is severely constrained by drought, especially if encountered during panicle initiation and flowering
By a molecular comparative analysis of drought tolerant, Nagina 22 (N22)[32,33,34,35] and sensitive rice cultivar, Pusa Basmati 1 (PB1)[36] we could delineate a multi-dimensional regulatory network wherein the miRNA nodes function as a junction associating rice copper and reactive oxygen species (ROS) homeostasis with drought tolerance in tolerant rice cultivar
Several rice cultivars have a natural capacity to tolerate drought stress conditions and their biology is of immense source of knowledge to understand the evolution of molecular nature of tolerance
Summary
Rice production is severely constrained by drought, especially if encountered during panicle initiation and flowering. By a molecular comparative analysis of drought tolerant, Nagina 22 (N22)[32,33,34,35] and sensitive rice cultivar, Pusa Basmati 1 (PB1)[36] we could delineate a multi-dimensional regulatory network wherein the miRNA nodes function as a junction associating rice copper and ROS homeostasis with drought tolerance in tolerant rice cultivar This naturally occurring schema involves the interplay of Cu-transporters, TF, miRNAs, Cu-requiring proteins and metabolic enzymes. This drought mediated copper deficiency up-regulates cultivar-specific drought responsive (CSDR)-miRNAs (miR408-3p, miR528-5p, miR398b, miR397a, miR1871, miR159f and miR2878-5p) via TF OsSPL9 [SQUAMOSA PROMOTER BINDING PROTEINS (SBP) like], which in turn down-regulates several genes coding for Cu-containing proteins (e.g. plantacyanins, laccases, Cu/Zn SODs etc.) This leads to ROS accumulation and enhanced stomata closure in the tolerant cultivar
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