Avenues for increasing salt tolerance of crops,and the role of physiologically based selection traits

Increased salt tolerance is needed for crops grown in areas at risk of salinisation. This requires new genetic sources of salt tolerance, and more efficient techniques for identifying salt-tolerant germplasm, so that new genes for tolerance can be introduced into crop cultivars. Screening a large number of genotypes for salt tolerance is not easy. Salt tolerance is achieved through the control of salt movement into and through the plant, and salt-specific effects on growth are seen only after long periods of time. Early effects on growth and metabolism are likely due to osmotic effects of the salt, that is to the salt in the soil solution. To avoid the necessity of growing plants for long periods of time to measure biomass or yield, practical selection techniques can be based on physiological traits. We illustrate this with current work on durum wheat, on selection for the trait of sodium exclusion. We have explored a wide range of genetic diversity, identified a new source of sodium exclusion, confirmed that the trait has a high heritability, checked for possible penalties associated with the trait, and are currently developing molecular markers. This illustrates the potential for marker-assisted selection based on sound physiological principles in producing salt-tolerant crop cultivars.     

A Single Species of Betasatellite is Prevalent in Chilli across North Central Pakistan and Shows Phylogeographic Segregation

Chilli leaf curl disease is an important constraint to production of chilli peppers ( Capsicum annum L.) across the Indian subcontinent and is caused by begomoviruses in association with betasatellites. Betasatellites are symptom modulating single-stranded DNA satellites associated with the majority of monopartite begomoviruses and are responsible for diseases of many crops including chilli peppers. Here, we have studied the diversity of a betasatellite of chillies in the Punjab and North Western Frontier Province of Pakistan. Sequence analysis of thirteen full-length clones showed that a single species of satellite, Chilli leaf curl betasatellite (ChLCB), is prevalent in chilli throughout the surveyed region. ChLCB has only been identified in Pakistan and infecting chilli. It thus probably represents a chilli adapted satellite. The ChLCBs fall into two groups, the first occurs in the less intensively cultivated north and shows a high level of sequence diversity (relative to the second group), while the second occurs in the southern cotton-growing areas and shows little sequence diversity. Between these two areas there is a region of overlap where both ChLCB types occur. The phylogeographic segregation of ChLCB we attribute to geographic isolation (in the north), leading to divergence and intensive cultivation (in the south), leading to homogenization. However, the lack of diversity (only a single species) bodes well for the prospects of achieving resistance to the disease by either conventional or pathogen-derived strategies.     

A Systematic Approach to Mapping Recessive Disease Genes in Individuals from Outbred Populations

The identification of recessive disease-causing genes by homozygosity mapping is often restricted by lack of suitable consanguineous families. To overcome these limitations, we apply homozygosity mapping to single affected individuals from outbred populations. In 72 individuals of 54 kindred ascertained worldwide with known homozygous mutations in 13 different recessive disease genes, we performed total genome homozygosity mapping using 250,000 SNP arrays. Likelihood ratio Z-scores (ZLR) were plotted across the genome to detect ZLR peaks that reflect segments of homozygosity by descent, which may harbor the mutated gene. In 93% of cases, the causative gene was positioned within a consistent ZLR peak of homozygosity. The number of peaks reflected the degree of inbreeding. We demonstrate that disease-causing homozygous mutations can be detected in single cases from outbred populations within a single ZLR peak of homozygosity as short as 2 Mb, containing an average of only 16 candidate genes. As many specialty clinics have access to cohorts of individuals from outbred populations, and as our approach will result in smaller genetic candidate regions, the new strategy of homozygosity mapping in single outbred individuals will strongly accelerate the discovery of novel recessive disease genes.     

Glycine betaine may have opposite effects on protein stability at high and low pH values

The compatible osmolyte glycine betaine (GB) is the most efficient osmoprotectant and best excluder from the protein surface. It can reverse protein aggregation and correct mutant protein defects and counter the harmful effects of urea and salts in vivo and in vitro. In this study we have investigated the pH dependence of the stabilizing effect of GB on three different proteins, namely, α-lactalbumin (α-LA), lysozyme and ribonuclease-A (RNase-A). We show here that (a) GB stabilizes RNase-A at all pH values, and (b) GB has opposite effects on two proteins at high pH and low pH values, namely, α-LA and lysozyme. This conclusion was reached by determining T_m (midpoint of denaturation), ΔH_m (denaturational enthalpy change at T_m), ΔC_p (constant-pressure heat capacity change) and ΔG_D^o (denaturational Gibbs energy change at 25 °C) of proteins in the presence of different GB concentrations. Another conclusion of this study is that ΔH_m and ΔC_p are not significantly changed in the presence of GB. This study suggests that other methylated glycine osmolytes may also behave in the same manner.     

Changes in rubisco content in relation to saccharides accumulation in wheat leaves during day

Two wheat varieties, T. durum (HD 4502) and T. aestivum (Kalyansona) were examined for photosynthesis rate and contents of sugars and rubisco protein in the flag leaf, at forenoon and afternoon at anthesis stage. A decrease in photosynthesis rate was observed in the afternoon compared to forenoon in both the varieties and was associated with an increase in non-reducing sugars and a decrease in rubisco content in the leaves.     

Angiopoietins have distinct modular domains essential for receptor binding,dimerization and superclustering

Angiopoietins are a recently discovered family of angiogenic factors that interact with the endothelial receptor tyrosine kinase Tie2, either as agonists (angiopoietin-1) or as context-dependent agonists/antagonists (angiopoietin-2). Here we show that angiopoietin-1 has a modular structure unlike any previously characterized growth factor. This modular structure consists of a receptor-binding domain, a dimerization motif and a superclustering motif that forms variable-sized multimers. Genetic engineering of precise multimers of the receptor-binding domain of angiopoietin-1, using surrogate multimerization motifs, reveals that tetramers are the minimal size required for activating endothelial Tie2 receptors. In contrast, engineered dimers can antagonize endothelial Tie2 receptors. Surprisingly, angiopoietin-2 has a modular structure and multimerization state similar to that of angiopoietin-1, and its antagonist activity seems to be a subtle property encoded in its receptor-binding domain.     

Genetic polymorphism of six DNA loci in six population groups of India

The genetic profile based on autosomal markers, four microsatellite DNA markers (D8S315, FES, D8S592, and D2S1328) and two minisatellite DNA markers (TPMT and PDGFA), were analyzed in six endogamous populations to examine the effect of geographic and linguistic affiliation on the genetic affinities among the groups. The six populations are from three different states of India and are linguistically different. Marathas from western India speak Marathi, an Indo-European language. Arayas, Muslims, Ezhavas, and Nairs from Kerala state of South India speak Malayalam, and Iyers from Tamil Nadu state speak Tamil. Genomic DNA was extracted from peripheral blood samples of random, normal, healthy individuals. Locus-specific PCR amplification was carried out, followed by electrophoresis of the amplicons and genotyping. All the loci were highly polymorphic and followed Hardy-Weinberg equilibrium, except for loci D8S315 and PDGFA in Iyers and Marathas, respectively. All six loci had high heterozygosity (average heterozygosity ranged from 0.73 to 0.76) and high polymorphism information content (0.57-0.90). The extent of gene differentiation among the six populations (G(ST) = 0.030) was greater than that for four Kerala populations (G(ST) = 0.011), suggesting proximity between the four Kerala populations. This result conforms with the cultural and linguistic background of the populations. The extent of diversity found among the populations probably resulted from the strict endogamous practices that they follow.     

Serum hormonal, electrolytes and trace element profiles in the rutting and non-rutting one-humped male camel (Camelus dromedarius)

The camel is known to be a seasonal breeder and, in the male camel, the breeding activity maximizes during the rutting period (winter and spring seasons). During the non-rutting period (summer and autumn), however, the breeding activity almost ceases completely. Serum steroid hormonal, electrolytes and trace element profiles were studied in 16 adult male camels aged 5-9 years, slaughtered during the rutting (n=8) and non-rutting periods (n=8). Moreover, testicular and epididymal tissue contents of electrolytes and trace elements were also studied during these two periods. Serum levels of testosterone, progesterone and T(4):T(3) ratio were higher in the rutting animals when compared to the non-rutting ones, while the reverse was true for serum T(3), T(4) and corticosterone levels (p<0.01). Among minerals, serum levels of sodium, calcium, copper and zinc were higher, while those of potassium were lower, in the rutting than non-rutting camels. In the testicular tissue, the levels of sodium, calcium, copper and iron were higher in the rutting group, while magnesium was higher in non-rutting one. In the epididymis, the tissue levels of chloride, iron and zinc were higher in the rutting than non-rutting period. These results demonstrate a clear evidence of the distribution of steroid hormones, electrolytes and trace elements forming and maintaining a certain level at two different physiological states in camels.     

Biotransformation of adrenosterone by filamentous fungus, Cunninghamella elegans

Microbial transformation of adrenosterone (1) by suspended-cell cultures of the filamentous fungus Cunninghamella elegans resulted in the production of five metabolites 2-6, which were identified as 9alpha-hydroxyadrenosterone (2), 11-ketotestosterone (3), 6beta-hydroxyadrenosterone (4), 9alpha-hydroxy-11-ketotestosterone (5), and 6beta-hydroxy-11-ketotestosterone (6). Structures of new metabolites 2, 5, and 6 were established by single-crystal X-ray diffraction analysis.