Showing papers by "Devinder Sandhu published in 2017"

Variable salinity responses of 12 alfalfa genotypes and comparative expression analyses of salt-response genes

Abstract: Twelve alfalfa genotypes that were selected for biomass under salinity, differences in Na and Cl concentrations in shoots and K/Na ratio were evaluated in this long-term salinity experiment. The selected plants were cloned to reduce genetic variability within each genotype. Salt tolerance (ST) index of the genotypes ranged from 0.39 to 1. The most salt-tolerant genotypes SISA14-1 (G03) and AZ-90ST (G10), the top performers for biomass, exhibited the least effect on shoot number and height. SISA14-1 (G03) accumulated low Na and Cl under salinity. Most genotypes exhibited a net reduction in shoot Ca, Mg, P, Fe, and Cu, while Mn and Zn increased under salinity. Salinity reduced foliar area and stomatal conductance; while net photosynthetic rate and transpiration were not affected. Interestingly, salinity increased chlorophyll and antioxidant capacity in most genotypes; however neither parameter correlated well to ST index. Salt-tolerant genotypes showed upregulation of the SOS1, SOS2, SOS3, HKT1, AKT1, NHX1, P5CS1, HSP90.7, HSP81.2, HSP71.1, HSPC025, OTS1, SGF29 and SAL1 genes. Gene expression analyses allowed us to classify genotypes based on their ability to regulate different components of the salt tolerance mechanism. Pyramiding different components of the salt tolerance mechanism may lead to superior salt-tolerant alfalfa genotypes.

The endogenous transposable element Tgm9 is suitable for generating knockout mutants for functional analyses of soybean genes and genetic improvement in soybean.

Abstract: In soybean, variegated flowers can be caused by somatic excision of the CACTA-type transposable element Tgm9 from Intron 2 of the DFR2 gene encoding dihydroflavonol-4-reductase of the anthocyanin pigment biosynthetic pathway. DFR2 was mapped to the W4 locus, where the allele containing Tgm9 was termed w4-m. In this study we have demonstrated that previously identified morphological mutants (three chlorophyll deficient mutants, one male sterile-female fertile mutant, and three partial female sterile mutants) were caused by insertion of Tgm9 following its excision from DFR2. Analyses of Tgm9 insertion sites among 105 independent mutants demonstrated that Tgm9 hops to all 20 soybean chromosomes from its original location on Chromosome 17. Some genomic regions are prone to increased Tgm9-insertions. Tgm9 transposed over 25% of the time into exon or intron sequences. Tgm9 is therefore suitable for generating an indexed insertional mutant collection for functional analyses of most soybean genes. Furthermore, desirable Tgm9-induced stable knockout mutants can be utilized in generating improved traits for commercial soybean cultivars.

Isolation and characterization of the aconitate hydratase 4 (Aco4) gene from soybean

Abstract: Aconitase catalyzes the reversible isomerization of two tricarboxylic acids, citrate and isocitrate, during the Krebs cycle. Five aconitase genes, namely, Aco1, Aco2, Aco3, Aco4, and Aco5, have bee...

Transposon-Based Functional Characterization of Soybean Genes

Abstract: Type II transposable elements that use a cut-and-paste mechanism for jumping from one genomic region to another are ideal for use in tagging and cloning genes. Precise excision from an insertion site in a mutant gene leads to regaining the wild-type function. Thus, the function of a gene can be established based on the mutant phenotype and the regaining of the wild-type phenotype following precise excision of the element. Heterologous type II transposable elements including the Ac/Ds system from maize, the miniature inverted repeat system, mPing from rice, and the Tnt1 retrotransposon from tobacco have been successfully applied in functional analyses of soybean genes. Although several endogenous transposable elements have been identified in soybean, evidence of an active type II transposable element in soybean was largely lacking. We have previously reported the isolation of the type II soybean transposon Tgm9 from intron II of the dihyroflavonol-4-reductase 2 (DFR2) gene of the W4 locus. Tgm9 is an active element and produces variegated flowers through somatic excision. Excision of the Tgm9 element from the progenitor cells of flower buds results in genotypes with purple flowers that are known as germinal revertants. The element was discovered from a commercial soybean cultivar, and the line carrying the element was termed T322. The T322 genome contains only one active Tgm9 copy in the W4 locus. In a recent study, the utility of Tgm9 was assessed by studying a set of random germinal revertants. The new mutations created following excision of Tgm9 from DFR2 were evaluated using a transposon display assay. This study revealed that Tgm9 transposes to all 20 soybean chromosomes from its original site in the DFR2 gene. Although Tgm9 exhibited preferential transposition to a few genomic regions, across the entire genome 25.7% of the new Tgm9 mutants were detected in exon or intron sequences. Thus, Tgm9 is a suitable endogenous type II transposon to generate an indexed insertional mutant collection for functional characterization of most of the soybean genes.