Spermidine exogenous application mollifies reproductive stage heat stress ramifications in rice.

Introduction: Rice productivity is severely hampered by heat stress (HS) which induces oxidative stress in this crop. This oxidative stress can be alleviated using various exogenous chemicals, including spermidine (Spd). Therefore, the present study was carried out to characterize HS components and to elucidate the role of exogenous Spd application in rice at the flowering stage. Methods: Two contrasting rice genotypes, i.e. Nagina22 (N22) and Pusa Basmati-1121 (PB-1121) were placed in temperature tunnels and exposed to HS (38-43°C) with and without Spd (1.5 mM) foliar application during the heading stage till the end of the anthesis stage. Result: Heat stress induced the production of H2O2 and thiobarbituric acid reactive substances, which resulted in lower photosynthesis, spikelet sterility, and reduced grain yield. Interestingly, foliar application of Spd induced antioxidant enzyme activities and thus increased total antioxidant capacity resulting in higher photosynthesis, spikelet fertility, and improved grain yield under HS in both genotypes. Under HS with Spd, higher sugar content was recorded as compared to HS alone, which maintained the osmotic equilibrium in leaf and spikelets. Spd application initiated in vivo polyamine biosynthesis, which increased endogenous polyamine levels. Discussion: This study corroborates that the exogenous application of Spd is promising in induction of antioxidant defence and ameliorating HS tolerance in rice via improved photosynthesis and transpiration. Thereby, the study proposes the potential application of Spd to reduce HS in rice under current global warming scenario.

Genome Editing Targets for Improving Nutrient Use Efficiency and Nutrient Stress Adaptation.

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.

Physiological and molecular implications of multiple abiotic stresses on yield and quality of rice.

Abiotic stresses adversely affect rice yield and productivity, especially under the changing climatic scenario. Exposure to multiple abiotic stresses acting together aggravates these effects. The projected increase in global temperatures, rainfall variability, and salinity will increase the frequency and intensity of multiple abiotic stresses. These abiotic stresses affect paddy physiology and deteriorate grain quality, especially milling quality and cooking characteristics. Understanding the molecular and physiological mechanisms behind grain quality reduction under multiple abiotic stresses is needed to breed cultivars that can tolerate multiple abiotic stresses. This review summarizes the combined effect of various stresses on rice physiology, focusing on grain quality parameters and yield traits, and discusses strategies for improving grain quality parameters using high-throughput phenotyping with omics approaches.

Role of protein phosphatases in the regulation of nitrogen nutrition in plants.

The reversible protein phosphorylation and dephosphorylation mediated by protein kinases and phosphatases regulate different biological processes and their response to environmental cues, including nitrogen (N) availability. Nitrate assimilation is under the strict control of phosphorylation-dephosphorylation mediated post-translational regulation. The protein phosphatase family with approximately 150 members in Arabidopsis and around 130 members in rice is a promising player in N uptake and assimilation pathways. Protein phosphatase 2A (PP2A) enhances the activation of nitrate reductase (NR) by deactivating SnRK1 and reduces the binding of inhibitory 14-3-3 proteins on NR. The functioning of nitrate transporter NPF6.3 is regulated by phosphorylation of CBL9 (Calcineurin B like protein 9) and CIPK23 (CBL interacting protein kinase 23) module. Phosphorylation by CIPK23 inhibits the activity of NPF6.3, whereas protein phosphatases (PP2C) enhance the NPF6.3-dependent nitrate sensing. PP2Cs and CIPK23 also regulate ammonium transporters (AMTs). Under either moderate ammonium supply or high N demand, CIPK23 is bound and inactivated by PP2Cs. Ammonium uptake is mediated by nonphosphorylated and active AMT1s. Whereas, under high ammonium availability, CIPK23 gets activated and phosphorylate AMT1;1 and AMT1;2 rendering them inactive. Recent reports suggest the critical role of protein phosphatases in regulating N use efficiency (NUE). In rice, PP2C9 regulates NUE by improving N uptake and assimilation. Comparative leaf proteome of wild type and PP2C9 over-expressing transgenic rice lines showed 30 differentially expressed proteins under low N level. These proteins are involved in photosynthesis, N metabolism, signalling, and defence.