Genomewide basis for nitrogen use efficiency in contrasting genotypes of rice
Rice is an ideal crop with huge germplasm diversity and post-genomic resources for improvement of nitrogen (N) use efficiency (NUE). There is a paucity of comparative studies on rice genotypes contrasting for NUE, especially with urea, the predominant fertilizer in rice growing countries. In this study, low urea-responsive transcriptomes of contrasting rice genotypes namely Nidhi (low NUE) and Panvel1 (high NUE) were compared. They were based on whole plants grown for 21 days in pots containing nutrient-depleted soil fertilized with normal (15 mM) and low urea (1.5 mM) media. There were 1497 and 2819 differentially expressed genes (DEGs) in Nidhi and Panvel1, respectively, of which 271 were common. Though 1226 DEGs were genotype-specific in Nidhi and 2548 in Panvel1, there was far higher commonality in underlying processes. High NUE is associated with the urea-responsive regulation of other nutrient transporters, miRNAs, transcription factors and better photosynthesis, water use efficiency and post translational modifications. Many of their genes co-localized to NUE QTLs on chromosomes 1, 3 and 9. Field evaluation of the contrasting genotypes under different doses of urea revealed better performance of Panvel1 in different agronomic parameters including grain yield, transport/uptake efficiencies and NUE. Comparison of our urea-based transcriptomes with our previous nitrate-based transcriptomes from the same contrasting rice genotypes revealed many common processes despite large differences in their expression profiles. Our model proposes that differential involvement of transporters and transcription factors among others contributes to better urea uptake, translocation, utilization, flower development and yield for high NUE. SummaryRice genotypes with contrasting urea use efficiency differ in the role of transporters, transcription factors, miRNAs, post-translational modifications, photosynthesis and water use efficiency