Regulation of sulfate uptake in carrot cells: Properties of a hypercontrolled variant

Genome-Wide Identification and Expansion Patterns of SULTR Gene Family in Gramineae Crops and Their Expression Profiles under Abiotic Stress in Oryza sativa

Sulfate transporters (SULTRs), also known as H+/SO42- symporters, play a key role in sulfate transport, plant growth and stress responses. However, the evolutionary relationships and functional differentiation of SULTRs in Gramineae crops are rarely reported. Here, 111 SULTRs were retrieved from the genomes of 10 Gramineae species, including Brachypodium disachyon, Hordeum vulgare, Setaria italica, Sorghum bicolor, Zea mays, Oryza barthii, Oryza rufipogon, Oryza glabbermia and Oryza sativa (Oryza sativa ssp. indica and Oryza sativa ssp. japonica). The SULTRs were clustered into five clades based on a phylogenetic analysis. Syntheny analysis indicates that whole-genome duplication/segmental duplication and tandem duplication events were essential in the SULTRs family expansion. We further found that different clades and orthologous groups of SULTRs were under a strong purifying selective force. Expression analysis showed that rice SULTRs with high-affinity transporters are associated with the functions of sulfate uptake and transport during rice seedling development. Furthermore, using Oryza sativa ssp. indica as a model species, we found that OsiSULTR10 was significantly upregulated under salt stress, while OsiSULTR3 and OsiSULTR12 showed remarkable upregulation under high temperature, low-selenium and drought stresses. OsiSULTR3 and OsiSULTR9 were upregulated under both low-selenium and high-selenium stresses. This study illustrates the expression and evolutionary patterns of the SULTRs family in Gramineae species, which will facilitate further studies of SULTR in other Gramineae species.

Selection of Daucus carota somatic hybrids using drug resistance markers and characterization of their mitochondrial genomes

Protoplasts from different Daucus carota L. cell strains carrying resistance to glyphosate, 5-methyltryptophan, sodium selenate or selenocystine were fused in three combinations using dextran. Clones were selected for both of the resistances carried by the individual parental strains in medium with both inhibitors. No doubly resistant colonies formed from unfused controls or from protoplasts from each individual parental strain alone. Suspension cultures from the selected clones contained predominantly the additive chromosome numbers of the parental strains. Apparently the four resistances used are expressed dominantly in fusion hybrids. Analysis of mitochondrial DNA showed that recombination occurred in one fusion combination since the mitochondrial DNA in the hybrid cells was different from that of either parent as shown by restriction endonuclease fragment analysis. Mitochondrial DNA in the other two somatic hybrid combinations was parental. Thus, a dominant, nuclear resistance marker system has been developed to select efficiently for somatic hybrids in which mitochondrial DNA recombination can be studied.

Sulfate Uptake and Its Regulation in Lemna paucicostata Hegelm. 6746

The results of studies of SO(4) (2-) uptake by Lemna paucicostata are most simply interpreted by the hypothesis that at least two components are involved, one saturating and one linear, ;nonsaturating.' The saturating component has a low K(m) and high specificity for SO(4) (2-). Uptake by the nonsaturating component is less affected by pH and temperature than is that of the saturating system. SO(4) (2-) efflux is not quantitatively important in Lemna under standard conditions (20 micromolar SO(4) (2-)) (Datko AH, SH Mudd 1980 Plant Physiol 65: 906-912). 55% of newly taken up (35)SO(4) (2-) enters a slowly turning over compartment (vacuole?); 45% remains in a compartment (cytoplasm?) in which it is rapidly metabolized to organic compounds.Growth in increased concentrations of SO(4) (2-) or cystine, but not methionine, down-regulates the saturating, but not the nonsaturating, system. Growth in limiting SO(4) (2-) up-regulates the saturating system. Overall, a 500-fold change was observed. Reciprocal inhibition experiments demonstrated that molybdate and SO(4) (2-) are taken up by a common mechanism, but growth in molybdate failed to up-regulate SO(4) (2-) uptake. Regulation by growth in SO(4) (2-) or cystine did not markedly affect uptake of phosphate or of several organic compounds.The saturating system contributes 99% of SO(4) (2-) uptake under standard conditions, providing sufficient SO(4) (2-) so it is not limiting. In nature the same system likely contributes at least 65 to 70%.

Characterization of a selenocystine-resistant carrot cell line : alterations in cystine and sulfate uptake

A selenocystine-resistant carrot cell line, C-1, was isolated from a haploid carrot (Daucus carota) cell culture, HA. The C-1 variant takes up cystine, but not cysteine, more slowly than does HA. The selenocystine resistance is maintained in culture in the absence of selection and is expressed in regenerated plants. Results based on chromatographic separation of sulfur metabolites from cells fed with [(35)S]cystine suggest a block either in the uptake or reduction of cystine in the variant. Both lines can grow on cystine as sole sulfur source. Growth of the HA line on cystine suppressed the development of sulfate uptake capacity (Furner, Sung 1982 Proc Natl Acad Sci USA 79: 1149-1153), while cystine-grown C-1 cells have high levels of sulfate uptake capacity.We suggest that the C-1 line, grown on cystine, accumulates an insufficient quantity of some sulfur metabolite, which is involved in the control of sulfate uptake, to suppress the uptake. C-1 grown on cystine is more sensitive than HA to growth inhibition by the sulfate analog selenate.