Identification and mapping of QTLs associated with drought tolerance traits in rice by a cross between Super Basmati and IR55419-04.

Water stress, in a climate change scenario is one of the major threats for sustainable rice productivity. Combining drought resistance with yield and desirable economic traits is the most promising solution for the researchers. Although several studies resulted in the identification of QTLs for drought resistance in rice, but none of them serve as a milestone. Therefore, there is always a quest to find the new QTLs. The present investigation was carried out to map QTLs involved in drought resistance and yield related parameter in a cross of IR55419-04 and Super Basmati. An F2 population of 418 individuals was used as the mapping population. The raised nursery was transplanted in lyzimeters. Two extreme sets of tolerant (23 Nos.) and sensitive (23 Nos.) individuals were selected based on total water uptake under water stress conditions. Two hundred thirty microsatellite markers staggered on the whole genome were used for identifying polymorphic markers between the two parents. The selected 73 polymorphic microsatellites were used to genotype individuals and were scattered on a distance of 1735 cM on all 12 linkage groups. QTL analysis was performed by using the WinQTL Cartographer 2.5 V. A total of 21 QTLs were detected using composite interval mapping. The QTLs relating to drought tolerance at the vegetative stage were found on chromosome 1. Novel genomic regions were detected in the marker interval RM520-RM143 and RM168-RM520. The region has a significant QTL qTWU3.1 for total water uptake. Root morphological trait QTLs were found on chromosome 3. QTLs responsible for additive effects were due to the alleles of the IR55419-04. These novel QTLs can be used for marker assisted breeding to develop new drought-tolerant rice varieties and fine mapping can be used to explore the functional relationship between the QTLs and phenotypic traits.

QTL mapping and candidate gene analysis of ferrous iron and zinc toxicity tolerance at seedling stage in rice by genome-wide association study.

BACKGROUND: Ferrous iron (Fe) and zinc (Zn) at high concentration in the soil cause heavy metal toxicity and greatly affect rice yield and quality. To improve rice production, understanding the genetic and molecular resistance mechanisms to excess Fe and Zn in rice is essential. Genome-wide association study (GWAS) is an effective way to identify loci and favorable alleles governing Fe and Zn toxicty as well as dissect the genetic relationship between them in a genetically diverse population. RESULTS: A total of 29 and 31 putative QTL affecting shoot height (SH), root length (RL), shoot fresh weight (SFW), shoot dry weight (SDW), root dry weight (RDW), shoot water content (SWC) and shoot ion concentrations (SFe or SZn) were identified at seedling stage in Fe and Zn experiments, respectively. Five toxicity tolerance QTL (qSdw3a, qSdw3b, qSdw12 and qSFe5 / qSZn5) were detected in the same genomic regions under the two stress conditions and 22 candidate genes for 10 important QTL regions were also determined by haplotype analyses. CONCLUSION: Rice plants share partial genetic overlaps of Fe and Zn toxicity tolerance at seedling stage. Candidate genes putatively affecting Fe and Zn toxicity tolerance identified in this study provide valuable information for future functional characterization and improvement of rice tolerance to Fe and Zn toxicity by marker-assisted selection or designed QTL pyramiding.

Impact of Pre-Anthesis Drought Stress on Physiology, Yield-Related Traits, and Drought-Responsive Genes in Green Super Rice.

Optimum soil water availability is vital for maximum yield production in rice which is challenged by increasing spells of drought. The reproductive stage drought is among the main limiting factors leading to the drastic reduction in grain yield. The objective of this study was to investigate the molecular and morphophysiological responses of pre-anthesis stage drought stress in green super rice. The study assessed the performance of 26 rice lines under irrigated and drought conditions. Irrigated treatment was allowed to grow normally, while drought stress was imposed for 30 days at the pre-anthesis stage. Three important physiological traits including pollen fertility percentage (PFP), cell membrane stability (CMS), and normalized difference vegetative index (NDVI) were recorded at anthesis stage during the last week of drought stress. Agronomic traits of economic importance including grain yield were recorded at maturity stage. The analysis of variance demonstrated significant variation among the genotypes for most of the studied traits. Correlation and principal component analyses demonstrated highly significant associations of particular agronomic traits with grain yield, and genetic diversity among genotypes, respectively. Our study demonstrated a higher drought tolerance potential of GSR lines compared with local cultivars, mainly by higher pollen viability, plant biomass, CMS, and harvest index under drought. In addition, the molecular basis of drought tolerance in GSR lines was related to upregulation of certain drought-responsive genes including OsSADRI, OsDSM1, OsDT11, but not the DREB genes. Our study identified novel drought-responsive genes (LOC_Os11g36190, LOC_Os12g04500, LOC_Os12g26290, and LOC_Os02g11960) that could be further characterized using reverse genetics to be utilized in molecular breeding for drought tolerance.

Identification of QTLs for rice grain size and weight by high-throughput SNP markers in the IR64 x Sadri population.

Grain appearance is one of the most important attributes of rice. It is determined by grain size, shape, and weight, which in turn influences the rice yield and market value. In this study, QTLs for grain length, grain width, grain length/width ratio, and grain weight were mapped using the high-throughput indica/indica SNP platforms. The population of the mega indica variety IR64 and the high-quality aromatic variety Sadri from Iran was phenotyped. Based on this phenotypic data, plants of 94 F2:3 families including both parents were selected. A linkage map analysis of 210 SNP markers identified 14 QTLs controlling the grain length, grain width, length/width ratio, and 1,000 grain weight. Among these 14, one important region containing the QTLs for all the four studies' traits was mapped on chromosome 8. It was derived from Sadri for the decreased length/width ratio and increased grain weight. This study demonstrated the speed and efficiency in using multiplex SNP genotyping for QTL analysis. Moreover, this study identified four novel QTLs (qGL8, qTGW8, qLWR8, and qGW8) sharing the same position on chromosome 8 which were linked with grain quality characteristics between one indica and one aromatic variety. It will enable more precise marker-assisted selection for grain weight, shape, and size. Further in-depth studies are required to dissect this region of interest and identify the related gene(s).

Identification of Candidate Genes for Salinity and Anaerobic Tolerance at the Germination Stage in Rice by Genome-Wide Association Analyses.

Multiple stress tolerance at the seed germination stage is crucial for better crop establishment in the direct-seeded rice ecosystem. Therefore, identifying rice genes/quantitative trait loci (QTLs) associated with salinity and anaerobic tolerance at the germination stage is a prerequisite for adaptive breeding. Here, we studied 498 highly diverse rice accessions Xian (Indica) and Geng (Japonica), and six traits that are highly associated with salinity and anaerobic tolerance at germination stage were measured. A high-density 2.8M Single Nucleotide Polymorphisms (SNP) genotype map generated from the 3,000 Rice Genomes Project (3KRGP) was used for mapping through a genome-wide association study. In total, 99 loci harboring 117 QTLs were detected in different populations, 54, 21, and 42 of which were associated with anaerobic, salinity, and combined (anaerobic and salinity) stress tolerance. Nineteen QTLs were close to the reported loci for abiotic stress tolerance, whereas two regions on chromosome 4 (qSGr4a/qCL4c/qRI4d and qAGr4/qSGr4b) and one region on chromosome 10 (qRI10/qCL10/ qSGr10b/qBM10) were associated with anaerobic and salinity related traits. Further haplotype analysis detected 25 promising candidates genes significantly associated with the target traits. Two known genes (OsMT2B and OsTPP7) significantly associated with grain yield and its related traits under saline and anaerobic stress conditions were identified. In this study, we identified the genes involved in auxin efflux (Os09g0491740) and transportation (Os01g0976100), whereas we identified multistress responses gene OsMT2B (Os01g0974200) and a major gene OsTPP7 (Os09g0369400) involved in anaerobic germination and coleoptile elongation on chromosome 9. These promising candidates provide valuable resources for validating potential salt and anaerobic tolerance genes and will facilitate direct-seeded rice breeding for salt and anaerobic tolerance through marker-assisted selection or gene editing.

Methionine Promotes the Growth and Yield of Wheat under Water Deficit Conditions by Regulating the Antioxidant Enzymes, Reactive Oxygen Species, and Ions.

The individual application of pure and active compounds such as methionine may help to address water scarcity issues without compromising the yield of wheat. As organic plant growth stimulants, amino acids are popularly used to promote the productivity of crops. However, the influence of the exogenous application of methionine in wheat remains elusive. The present investigation was planned in order to understand the impact of methionine in wheat under drought stress. Two wheat genotypes were allowed to grow with 100% field capacity (FC) up to the three-leaf stage. Twenty-five-day-old seedlings of two wheat genotypes, Galaxy-13 and Johar-16, were subjected to 40% FC, denoted as water deficit-stress (D), along with 100% FC, called control (C), with and without L-methionine (Met; 4 mM) foliar treatment. Water deficit significantly reduced shoot length, shoot fresh and dry weights, seed yield, photosynthetic, gas exchange attributes except for transpiration rate (E), and shoot mineral ions (potassium, calcium, and phosphorus) in both genotypes. A significant increase was recorded in superoxide dismutase (SOD), catalase (CAT), hydrogen peroxide (H2O2), malondialdehyde (MDA), and sodium ions (Na+) due to water deficiency. However, foliar application of Met substantially improved the studied growth, photosynthetic, and gas exchange attributes with water deficit conditions in both genotypes. The activities of SOD, POD, and CAT were further enhanced under stress with Met application. Met improved potassium (K), calcium (Ca2+), and phosphorus (P) content. In a nutshell, the foliar application of Met effectively amended water deficit stress tolerance by reducing MDA and H2O2 content under water deficit conditions in wheat plants. Thus, we are able to deduce a positive association between Met-induced improved growth attributes and drought tolerance.

Genome-wide association mapping of aluminum toxicity tolerance and fine mapping of a candidate gene for Nrat1 in rice.

Aluminum (Al) stress is becoming the major limiting factor in crop production in acidic soils. Rice has been reported as the most Al-tolerant crop and the capacity of Al toxicity tolerance is generally evaluated by comparing root growth under Al stress. Here, we performed an association mapping of Al toxicity tolerance using a core collection of 211 indica rice accessions with 700 K high quality SNP data. A total of 21 putative QTL affecting shoot height (SH), root length (RL), shoot fresh weight (SFW), shoot dry weight (SDW), root dry weight (RDW) and shoot water content (SWC) were identified at seedling stage, including three QTL detected only under control condition, eight detected only under Al stress condition, ten simultaneously detected in both control and Al stress conditions, and seven were identified by stress tolerance index of their corresponding traits. Total of 21 candidate genes for 7 important QTL regions associated with Al toxicity tolerance were identified based on combined haplotype analysis and functional annotation, and the most likely candidate gene(s) for each important QTL were also discussed. Also a candidate gene Nrat1 on chromosome 2 was further fine-mapped using BSA-seq and linkage analysis in the F2 population derived from the cross of Al tolerant accession CC105 and super susceptible accession CC180. A new non-synonymous SNP variation was observed at Nrat1 between CC105 and CC180, which resulted in an amino-acid substitution from Ala (A) in CC105 to Asp (D) in CC180. Haplotype analysis of Nrat1 using 327 3K RGP accessions indicated that minor allele variations in aus and indica subpopulations decreased Al toxicity tolerance in rice. The candidate genes identified in this study provide valuable information for improvement of Al toxicity tolerance in rice. Our research indicated that minor alleles are important for QTL mapping and its application in rice breeding when natural gene resources are used.

Identification of QTN and candidate genes for Salinity Tolerance at the Germination and Seedling Stages in Rice by Genome-Wide Association Analyses.

To facilitate developing rice varieties tolerant to salt stress, a panel of 208 rice mini-core accessions collected from 25 countries were evaluated for 13 traits associated with salt tolerance (ST) at the germination and seedling stages. The rice panel showed tremendous variation for all measured ST traits and eight accessions showing high levels of ST at either and/or both the germination and seedling stages. Using 395,553 SNP markers covering ~372 Mb of the rice genome and multi-locus mixed linear models, 20 QTN associated with 11 ST traits were identified by GWAS, including 6 QTN affecting ST at the germination stage and 14 QTN for ST at the seedling stage. The integration of bioinformatic with haplotype analyses for the ST QTN lets us identify 22 candidate genes for nine important ST QTN (qGR3, qSNK1, qSNK12, qSNC1, qSNC6, qRNK2, qSDW9a, qSST5 and qSST9). These candidate genes included three known ST genes (SKC1, OsTZF1 and OsEATB) for QTN qSNK1 qSST5 and qSST9. Candidate genes showed significant phenotypic differences in ST traits were detected between or among 2-4 major haplotypes. Thus, our results provided useful materials and genetic information for improving rice ST in future breeding and for molecular dissection of ST in rice.