Seedling-stage salinity tolerance in rice: Decoding the role of transcription factors.

Rice is an important staple food crop that feeds over half of the human population, particularly in developing countries. Increasing salinity is a major challenge for continuing rice production. Though rice is affected by salinity at all the developmental stages, it is most sensitive at the early seedling stage. The yield thus depends on how many seedlings can withstand saline water at the stage of transplantation, especially in coastal farms. The rapid development of "omics" approaches has assisted researchers in identifying biological molecules that are responsive to salt stress. Several salinity-responsive quantitative trait loci (QTL) contributing to salinity tolerance have been identified and validated, making it essential to narrow down the search for the key genes within QTLs. Owing to the impressive progress of molecular tools, it is now clear that the response of plants toward salinity is highly complex, involving multiple genes, with a specific role assigned to the repertoire of transcription factors (TF). Targeting the TFs for improving salinity tolerance can have an inbuilt advantage of influencing multiple downstream genes, which in turn can contribute toward tolerance to multiple stresses. This is the first comparative study for TF-driven salinity tolerance in contrasting rice cultivars at the seedling stage that shows how tolerant genotypes behave differently than sensitive ones in terms of stress tolerance. Understanding the complexity of salt-responsive TF networks at the seedling stage will be helpful to alleviate crop resilience and prevent crop damage at an early growth stage in rice.

Organ-specific expression of genes involved in iron homeostasis in wheat mutant lines with increased grain iron and zinc content.

Background: Iron deficiency is a well-known nutritional disorder, and the imbalance of trace-elements, specifically iron, is the most common nutrient deficiency of foods across the world, including in Kazakhstan. Wheat has significant nutritional relevance, especially in the provision of iron, however many bread wheat varieties have low iron despite the need for human nourishment. In this study, the expression profiles of wheat homologous genes related to iron homeostasis were investigated. The work resulted in the development of two new M5 mutant lines of spring bread wheat through gamma-irradiation (200 Gy) with higher grain iron and zinc content, lower phytic acid content, and enhanced iron bioavailability compared to the parent variety. Mutant lines were also characterized by higher means of yield associated traits such as grain number per main spike, grain weight per main spike, grain weight per plant, and thousand-grain weight. Methods: The homologous genes of bread wheat from several groups were selected for gene expression studies exploring the tight control of iron uptake, translocation rate and accumulation in leaves and roots, and comprised the following: (1) S-adenosylmethionine synthase (SAMS), nicotianamine synthase (NAS1), nicotianamine aminotransferase (NAAT), deoxymugineic acid synthetase (DMAS), involved in the synthesis and release of phytosiderophores; (2) transcription factor basic helix-loop-helix (bHLH); (3) transporters of mugineic acid (TOM), involved in long-distance iron transport; (4) yellow stripe-like (YSlA), and the vacuolar transporter (VIT2), involved in intracellular iron transport and storage; and lastly (5) natural resistance-associated macrophage protein (NRAMP) and ferritin (Fer1A). Results: The wheat homologous genes TaSAMS, TaNAS1, and TaDMAS, were significantly up-regulated in the roots of both mutant lines by 2.1-4.7-fold compared to the parent variety. The combined over-expression of TaYSlA and TaVIT2 was also revealed in the roots of mutant lines by 1.3-2.7-fold. In one of the mutant lines, genes encoding intracellular iron transport and storage genes TaNRAMP and TaFer1A-D showed significant up-regulation in roots and leaves (by 1.4- and 3.5-fold, respectively). The highest expression was recorded in the transcription factor TabHLH, which was expressed 13.1- and 30.2-fold in the roots of mutant lines. Our research revealed that genotype-dependent and organ-specific gene expression profiles can provide new insights into iron uptake, translocation rate, storage, and regulation in wheat which aid the prioritization of gene targets for iron biofortification and bioavailability.

Mutation Associated with Orange Fruit Color Increases Concentrations of ß-Carotene in a Sweet Pepper Variety (Capsicum annuum L.).

Pepper is the second most important vegetable crop in Bulgarian agriculture and has become the subject of extensive breeding programs that frequently employ induced mutagenesis. The success of breeding programs can be enhanced by the efficient and integral application of different biochemical and molecular methods to characterize specific mutant alleles. On the other hand, identifying new cost-effective methods is important under a limited-resources environment. In this paper we compare the levels of five health-related carotenoid compounds of fruits (α-carotene, ß-carotene, lutein, ß-cryptoxanthin, zeaxanthin) between a mutant variety Oranzheva kapia (possessing high ß-carotene concentration) and a corresponding initial pepper variety Pazardzhishka kapia 794. Both varieties are intended for fresh consumption. Pepper is a major natural source of ß-carotene. It was observed that fruit at both commercial and botanical maturity from mutant variety had greater α-carotene and ß-carotene concentrations to the initial variety (7.49 and 1.94 times higher, respectively) meaning that the mutant was superior in fruit quality to the initial genotype. Two hydroxylase enzymes, converting α- and ß-carotene to lutein and zeaxanthin, respectively, are known to exist in pepper and are encoded by two genes on chromosomes 3 and 6-CrtZchr03 and CrtZchr06. The molecular characterization of the mutant variety through locus-specific Polymerase chain reaction amplification, gene cloning and sequencing as well as expression was performed. Our results suggest that the increased ß-carotene accumulation in the mutant variety Oranzheva kapia results from a biosynthetic pathway breakdown due to deletion of CrtZchr03 gene.

Technical note: Gamma irradiation induces changes of phenotypic and agronomic traits in wheat (Triticum turgidum ssp. durum).

WHEAT VAR: CIRNO C2008 was irradiated with gamma rays at 100, 200, and 300 Gy. The irradiated plants obtained at 300 Gy (M1) showed a significant reduction (compared to M0 plants) in germination (i.e. 3.8% at day 5), survival percentage (48%), and plant height (63.3%). Thus, the Probit analysis showed an LD50 of 287.80 Gy. Besides, these irradiated plants, in the field, showed a significant increase (compared to M0 plants) in days to spike initiation (16 days), and maturation (14 days). On the other hand, in the field, fourteen chlorophyll mutants were found (at a different frequency) in the M2 generation, such as Albina, Anthocyanin, Chlorina, Maculata, Tigrina, Striata, Viridis, Viridoalbina, Alboviridis, Xantha, Xanthviridis, Xanthalba, Viridoxantha, and Orange stem. In addition, mutants with changes in agronomic and morphological traits were observed. This nuclear technique is an alternative to obtain promising mutant lines that can be used directly as a variety and/or as parental to transfer these traits to other varieties.

The Effect of Single and Combined Use of Gamma Radiation and Ethylmethane Sulfonate on Early Growth Parameters in Sorghum.

Success in inducing genetic variation through mutagenic agents is dependent on the source and dose of application. The objective of this study was to determine the optimum doses of a single and combined use of gamma radiation and ethylmethane sulfonate (EMS) for effective mutation breeding in sorghum. The study involved two concurrent experiments as follows: in experiment I, the seeds of four sorghum genotypes ('Parbhani Moti', 'Parbhani Shakti', 'ICSV 15013', and 'Macia') were treated using gamma radiation (0, 300, 400, 500 and 600 Gy), EMS (0, 0.5 and 1.0%), and gamma radiation followed by EMS (0 and 300 Gy and 0.1% EMS; 400 Gy and 0.05% EMS). In experiment II, the seeds of two genotypes ('Macia' and 'Red sorghum') were treated with seven doses of gamma radiation only (0, 100, 200, 300, 400, 500 and 600 Gy). Overall, the combined applied doses of gamma radiation and EMS are not recommended due to poor seedling emergence and seedling survival rate below LD50. The best dosage of gamma radiation for genotypes Red sorghum, Parbhani Moti, Macia, ICSV 15013 and Parbhani Shakti ranged between 392 and 419 Gy, 311 and 354 Gy, 256 and 355 Gy, 273 and 304 Gy, and 266 and 297 Gy, respectively. The EMS optimum dosage ranges for genotypes Parbhani Shakti, ICSV 15013, Parbhani Moti and Macia were between 0.41% and 0.60%, 0.48% and 0.58%, 0.46% and 0.51%, and 0.36% and 0.45%, respectively. The above dose rates are useful to induce genetic variation in the tested sorghum genotypes for greater mutation events in sorghum breeding programs.

Mutant Lines of Spring Wheat with Increased Iron, Zinc, and Micronutrients in Grains and Enhanced Bioavailability for Human Health.

Deficiency of metals, primarily Fe and Zn, affects over half of the world's population. Human diets dominated by cereal products cause micronutrient malnutrition, which is common in many developing countries where populations depend heavily on staple grain crops such as wheat, maize, and rice. Biofortification is one of the most effective approaches to alleviate malnutrition. Genetically stable mutant spring wheat lines (M7 generation) produced via 100 or 200 Gy gamma treatments to broaden genetic variation for grain nutrients were analyzed for nutritionally important minerals (Ca, Fe, and Zn), their bioavailability, and grain protein content (GPC). Variation was 172.3-883.0 mg/kg for Ca, 40.9-89.0 mg/kg for Fe, and 22.2-89.6 mg/kg for Zn. In mutant lines, among the investigated minerals, the highest increases in concentrations were observed in Fe, Zn, and Ca when compared to the parental cultivar Zhenis. Some mutant lines, mostly in the 100 Gy-derived germplasm, had more than two-fold higher Fe, Zn, and Ca concentrations, lower phytic acid concentration (1.4-2.1-fold), and 6.5-7% higher grain protein content compared to the parent. Variation was detected for the molar ratios of Ca:Phy, Phy:Fe, and Phy:Zn (1.27-10.41, 1.40-5.32, and 1.78-11.78, respectively). The results of this study show how genetic variation generated through radiation can be useful to achieve nutrient biofortification of crops to overcome human malnutrition.