Genetic Architecture of Aluminum Tolerance in Rice (Oryza sativa) Determined through Genome-Wide Association Analysis and QTL Mapping

Aluminum (Al) toxicity is a primary limitation to crop productivity on acid soils, and rice has been demonstrated to be significantly more Al tolerant than other cereal crops. However, the mechanisms of rice Al tolerance are largely unknown, and no genes underlying natural variation have been reported. We screened 383 diverse rice accessions, conducted a genome-wide association (GWA) study, and conducted QTL mapping in two bi-parental populations using three estimates of Al tolerance based on root growth. Subpopulation structure explained 57% of the phenotypic variation, and the mean Al tolerance in Japonica was twice that of Indica. Forty-eight regions associated with Al tolerance were identified by GWA analysis, most of which were subpopulation-specific. Four of these regions co-localized with a priori candidate genes, and two highly significant regions co-localized with previously identified QTLs. Three regions corresponding to induced Al-sensitive rice mutants (ART1, STAR2, Nrat1) were identified through bi-parental QTL mapping or GWA to be involved in natural variation for Al tolerance. Haplotype analysis around the Nrat1 gene identified susceptible and tolerant haplotypes explaining 40% of the Al tolerance variation within the aus subpopulation, and sequence analysis of Nrat1 identified a trio of non-synonymous mutations predictive of Al sensitivity in our diversity panel. GWA analysis discovered more phenotype–genotype associations and provided higher resolution, but QTL mapping identified critical rare and/or subpopulation-specific alleles not detected by GWA analysis. Mapping using Indica/Japonica populations identified QTLs associated with transgressive variation where alleles from a susceptible aus or indica parent enhanced Al tolerance in a tolerant Japonica background. This work supports the hypothesis that selectively introgressing alleles across subpopulations is an efficient approach for trait enhancement in plant breeding programs and demonstrates the fundamental importance of subpopulation in interpreting and manipulating the genetics of complex traits in rice

Genome-wide association mapping reveals a rich genetic architecture of complex traits in Oryza sativa

Asian rice, Oryza sativa is a cultivated, inbreeding species that feeds over half of the world's population. Understanding the genetic basis of diverse physiological, developmental, and morphological traits provides the basis for improving yield, quality and sustainability of rice. Here we show the results of a genome-wide association study based on genotyping 44,100 SNP variants across 413 diverse accessions of O. sativa collected from 82 countries that were systematically phenotyped for 34 traits. Using cross-population-based mapping strategies, we identified dozens of common variants influencing numerous complex traits. Significant heterogeneity was observed in the genetic architecture associated with subpopulation structure and response to environment. This work establishes an open-source translational research platform for genome-wide association studies in rice that directly links molecular variation in genes and metabolic pathways with the germplasm resources needed to accelerate varietal development and crop improvement

Genome-wide association mapping identifies a new arsenate reductase enzyme critical for limiting arsenic accumulation in plants

Inorganic arsenic is a carcinogen, and its ingestion through foods such as rice presents a significant risk to human health. Plants chemically reduce arsenate to arsenite. Using genome-wide association (GWA) mapping of loci controlling natural variation in arsenic accumulation in Arabidopsis thaliana allowed us to identify the arsenate reductase required for this reduction, which we named High Arsenic Content 1 (HAC1). Complementation verified the identity of HAC1, and expression in Escherichia coli lacking a functional arsenate reductase confirmed the arsenate reductase activity of HAC1. The HAC1 protein accumulates in the epidermis, the outer cell layer of the root, and also in the pericycle cells surrounding the central vascular tissue. Plants lacking HAC1 lose their ability to efflux arsenite from roots, leading to both increased transport of arsenic into the central vascular tissue and on into the shoot. HAC1 therefore functions to reduce arsenate to arsenite in the outer cell layer of the root, facilitating efflux of arsenic as arsenite back into the soil to limit both its accumulation in the root and transport to the shoot. Arsenate reduction by HAC1 in the pericycle may play a role in limiting arsenic loading into the xylem. Loss of HAC1-encoded arsenic reduction leads to a significant increase in arsenic accumulation in shoots, causing an increased sensitivity to arsenate toxicity. We also confirmed the previous observation that the ACR2 arsenate reductase in A. thaliana plays no detectable role in arsenic metabolism. Furthermore, ACR2 does not interact epistatically with HAC1, since arsenic metabolism in the acr2 hac1 double mutant is disrupted in an identical manner to that described for the hac1 single mutant. Our identification of HAC1 and its associated natural variation provides an important new resource for the development of low arsenic-containing food such as rice

Conoscenza, riordino e tutela del territorio nella programmazione e nell'intervento della Regione Sicilia

Cannizzaro S. \ue8 autore dei due paragrafi IV (La carta dell'uso del suolo) e V (Le aree protette)

La regione costiera della Tunisia tra congestione e sviluppo

Cannizzaro Salvatore \ue8 autore dei paragrafi I (Caratteri ambientali ed antropici generali)e VI (L'industrializzazione costiera) del suindicato articolo

Coronary flow reserve in patients with primary biliary cholangitis

Background: It is still not clear whether primary biliary cholangitis (PBC) is associated with abnormalities of the cardiovascular system. We aimed to assess the relationship between PBC and coronary flow reserve (CFR). Methods: Our inclusion criterion was a diagnosis of PBC with no clinical evidence of heart disease or metabolic syndrome. Coronary flow velocity in the left anterior descending coronary artery was measured using transthoracic Doppler echocardiography at rest (DFVr), and during adenosine infusion (DFVh). The corrected CFR (cCFR) was defined as the ratio of DFVh to DFVr corrected for cardiac workload (cDFVr). Microvascular resistance was also assessed in baseline (BMR) and hyperemic conditions (HMR). Results: 37 PBC patients and 37 sex- and age-matched controls were considered. The cCFR was significantly lower in PBC patients (2.8 ± 0.7 vs. 3.7 ± 0.7, p < 0.0001), and abnormal (≤2.5) in 13 (35%) of them, but in none of the controls (p < 0.0001). The cDFVr was higher in patients with abnormal cCFR (29.0 ± 6.0 vs. 20.4 ± 4.5 cm/sec, p < 0.0001). The CFR and cCFR did not correlate with any characteristics of PBC, comorbidities or Framingham risk scores. The BMR and HMR correlated with time since PBC diagnosis and duration of symptoms. Conclusion: The CFR is reduced in PBC, apparently due to mechanisms correlating with the time since diagnosis. In particular, the higher cDFVr with a lower basal resistance in patients with cCFR ≤ 2.5 suggests a compensatory mechanism against any cardiomyocyte bioenergetics impairment