The NIN-LIKE PROTEIN (NLP) family of transcription factors were identified as nitrate-responsive ciselement (NRE)-binding proteins, which function as transcriptional activators in the nitrate-regulated expression of downstream genes. this study was aimed at genome-wide analysis of NLP gene family in rice and the expression profiling of NLPs in response to nitrogen (N) supply and deficiency in rice genotypes with contrasting N use efficiency (NUE). Based on in silico analysis, 6 NLP genes (including alternative splice forms 11 NLPs) were identified from rice. Expression of NLPs was promoted by nitrate supply as well as N deficiency (NLP1, NLP3, NLP4 and NLP5). Four rice genotypes APO (high NUE under sufficient N), IR83929-B-B-291-3-1-1 (IR-3-1-1), Nerica-L-42 (NL-42) (High NUE at low N), and Pusa Basmati 1 (PB1, low NUE) to correlate traits governing NUE and expression of NLPs. Analysis of rate of nitrate uptake and expression of N assimilatory and uptake genes established that IR-3-1-1 has high uptake and assimilation efficiency, translating into high NUE, whereas PB1 is efficient in uptake only when N availability is high. Along with the transcriptional upregulation of NLPs, genotype IR-3-1-1, displayed highest expression of OsNRT1.1B gene, the closest rice homologue of nitrate transceptor AtNRT1.1 and plays major role in nitrate uptake, translocation and signaling in rice. The results showed that high NUE rice genotypes has both high Nitrogen uptake efficiency (NUpE) and Nitrogen utilization efficiency (NUtE), resulting from the effective and coordinated signal transduction network involving the rice homologue of nitrate transceptor OsNRT1.1B, the probable primary nitrate response (PNR) regulator OsNLP1 and the master response regulator OsNLP3, a homologue of AtNLP6/7. Nitrogen (N) is an essential nutrient and major component of proteins, chlorophyll, nucleotides and plant hormones, and therefore has immense role in determining plant growth and economic yield 1,2. In order to meet the food demand of ever-growing human population, enormous amounts of N fertilizers are applied inorder to tap the maximum crop yield potential worldwide 3. The global demand for N fertilizers in 2014 was 1.13 M tonnes and is projected to grow at approximately 1.4% per year, reaching 1.22 M tonnes by 2020 4. On the other hand, around 50% of the applied N fertilizer is lost to the environment depending on the cropping conditions and plant species. The loss of fertilizer N results in contamination of soil water and water bodies and production of nitrogenous greenhouse gases like nitrous oxide (N 2 O) which has high global warming potential 5. Nitrogen use efficiency (NUE) of rice is particularly low (around 40%), though genetic variation for the trait has been reported 6. Consequently, there is an impending requirement to improve the NUE of rice to maintain the steadiness of high crop yields visa vis low N fertilizer inputs 7. Transgenic manipulation is one of the potent way to achieve the current demand for high NUE, which necessitates...

In recent years, the development of RNA-guided genome editing (CRISPR-Cas9 technology) has revolutionized plant genome editing. Under nutrient deficiency conditions, different transcription factors and regulatory gene networks work together to maintain nutrient homeostasis. Improvement in the use efficiency of nitrogen (N), phosphorus (P) and potassium (K) is essential to ensure sustainable yield with enhanced quality and tolerance to stresses. This review outlines potential targets suitable for genome editing for understanding and improving nutrient use (NtUE) efficiency and nutrient stress tolerance. The different genome editing strategies for employing crucial negative and positive regulators are also described. Negative regulators of nutrient signalling are the potential targets for genome editing, that may improve nutrient uptake and stress signalling under resource-poor conditions. The promoter engineering by CRISPR/dead (d) Cas9 (dCas9) cytosine and adenine base editing and prime editing is a successful strategy to generate precise changes. CRISPR/dCas9 system also offers the added advantage of exploiting transcriptional activators/repressors for overexpression of genes of interest in a targeted manner. CRISPR activation (CRISPRa) and CRISPR interference (CRISPRi) are variants of CRISPR in which a dCas9 dependent transcription activation or interference is achieved. dCas9-SunTag system can be employed to engineer targeted gene activation and DNA methylation in plants. The development of nutrient use efficient plants through CRISPR-Cas technology will enhance the pace of genetic improvement for nutrient stress tolerance of crops and improve the sustainability of agriculture.

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To maintain yield stability and environmental sustainability of rice cultivation, improvement in nitrogen use efficiency (NUE) is essential. We identified rice genotypes showing high NUE in control (N120) and N deficient (N0) field conditions by analyzing NUE parameters and different contributing traits. In the first season, genotypes BAM-3181, BAM-4797, BAM-3154, NL-26 IR-83929-B-B-291-3-1-1 (IR-3-1-1), APO and NERICA-L-42 showed high biomass, panicle yield and N utilization efficiency (NutE) at low N field conditions. Reproductive stage N assimilatory and signaling gene expression was correlated to the variation in NUtE. The sequence variation in N metabolism and signaling (NLP) genes were analyzed in selected genotypes (APO and NERICA-L-42). Significant non-synonymous SNPs were found in NPF2.2, PTR2, NGR9 (DEP1), Fd-GOGAT, NLP3, NLP4 and NLP5 genes of APO, NERICA-L-42 and w.r.to japonica genotype Nipponbare. The significant variation in reproductive stage gene expression and changes in amino acid sequence of NLP3, NLP4, NLP5 among rice genotypes differing in NUE is an unexplored and potent genome editing target for high NUE in rice. The non-synonymous SNPs identified in the study will be important genomic resources for improving rice NUE.

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