SULTR3;1 is a chloroplast‐localized sulfate transporter in Arabidopsis thaliana

Plants play a prominent role as sulfur reducers in the global sulfur cycle. Sulfate, the major form of inorganic sulfur utilized by plants, is absorbed and transported by specific sulfate transporters into plastids, especially chloroplasts, where it is reduced and assimilated into cysteine before entering other metabolic processes. How sulfate is transported into the chloroplast, however, remains unresolved; no plastid‐localized sulfate transporters have been previously identified in higher plants. Here we report that SULTR3;1 is localized in the chloroplast, which was demonstrated by SULTR3;1‐GFP localization, Western blot analysis, protein import as well as comparative analysis of sulfate uptake by chloroplasts between knockout mutants, complemented transgenic plants, and the wild type. Loss of SULTR3;1 significantly decreases the sulfate uptake of the chloroplast. Complementation of the sultr3;1 mutant phenotypes by expression of a 35S‐SULTR3;1 construct further confirms that SULTR3;1 is one of the transporters responsible for sulfate transport into chloroplasts.     

MHC‐disassortative mate choice and inbreeding avoidance in a solitary primate

Sexual selection theory suggests that choice for partners carrying dissimilar genes at the major histocompatibility complex (MHC) may play a role in maintaining genetic variation in animal populations by limiting inbreeding or improving the immunity of future offspring. However, it is often difficult to establish whether the observed MHC dissimilarity among mates drives mate choice or represents a by‐product of inbreeding avoidance based on MHC‐independent cues. Here, we used 454‐sequencing and a 10‐year study of wild grey mouse lemurs (Microcebus murinus), small, solitary primates from western Madagascar, to compare the relative importance on the mate choice of two MHC class II genes, DRB and DQB, that are equally variable but display contrasting patterns of selection at the molecular level, with DRB under stronger diversifying selection. We further assessed the effect of the genetic relatedness and of the spatial distance among candidate mates on the detection of MHC‐dependent mate choice. Our results reveal inbreeding avoidance, along with disassortative mate choice at DRB, but not at DQB. DRB‐disassortative mate choice remains detectable after excluding all related dyads (characterized by a relatedness coefficient r > 0), but varies slightly with the spatial distance among candidate mates. These findings suggest that the observed deviations from random mate choice at MHC are driven by functionally important MHC genes (like DRB) rather than passively resulting from inbreeding avoidance and further emphasize the need for taking into account the spatial and genetic structure of the population in correlative tests of MHC‐dependent mate choice.     

Phylogeography of Sophora davidii (Leguminosae) across the ‘Tanaka‐Kaiyong Line’, an important phytogeographic boundary in Southwest China

The ‘Tanaka‐Kaiyong Line’ (TKL) is a major phytogeographic boundary in Southwest China, separating East Asia's Sino‐Himalayan and Sino‐Japanese Floras. However, little is known about the importance of this boundary in promoting intraspecific phylogeographic subdivision and divergence. Using chloroplast (cpDNA) and nuclear‐intron (nDNA) sequence data, we reconstructed the population history of Sophora davidii, a drought‐tolerant riparian shrub widely distributed on either side of the TKL. Specifically, we aimed at testing two long‐standing explanations for possible vicariant events across the TKL: (i) Late Pliocene (c. 3 Ma) geological uplift of the eastern Qinghai‐Tibetan Plateau (QTP) or (ii) a sharp environmental gradient associated with the establishment of different monsoon regimes on either side of the TKL during the (Late) Pleistocene. Our genealogical analyses detected a major west–east split in cpDNA, geographically largely consistent with the TKL, and dated to c. 1.28 Ma (95% HPD: 0.21–2.96 Ma), hence postdating the latest phase of eastern QTP uplift. Furthermore, integrating cpDNA phylogeographic patterns with mismatch analyses, we found multiple refugial isolation and long‐term demographic stability of populations in the west (Hengduan Mountain Range) compared with extensive range expansions in the east, possibly during the last glacial period(s) and followed by differentiation into regional sublineages (southeast: Yunnan‐Guizhou Plateau vs. northeast: Qinling Mts./Loess Plateau). Although nuclear differentiation was less marked, the geographical pattern of nDNA haplotypes provided some further indication of the species' eastward expansion, possibly from source populations located just east of the TKL (lower Jinshajiang region). Overall, the present data reject the geological (tectonic) explanation for the TKL and, instead, provide supportive evidence for its role as a climatically driven barrier to present‐day plant dispersal. In addition, our study highlights changing temperatures and vegetation types during the last glacial period(s), along with aspects of regional topography, to be important determinants of the glacial eastward expansion of S. davidii. In consequence, our study lends support to a ‘glacial out‐of‐Hengduan Mts’. hypothesis for the xerophytic‐riparian flora of Southwest China, which in turn is inconsistent with the traditional view of the TKL as a ‘classical’ vicariant‐biogeographic boundary.     

Nuclear and chloroplast DNA phylogeography reveals Pleistocene divergence and subsequent secondary contact of two genetic lineages of the tropical rainforest tree species Shorea leprosula (Dipterocarpaceae) in South‐East Asia

Tropical rainforests in South‐East Asia have been affected by climatic fluctuations during past glacial eras. To examine how the accompanying changes in land areas and temperature have affected the genetic properties of rainforest trees in the region, we investigated the phylogeographic patterns of a widespread dipterocarp species, Shorea leprosula. Two types of DNA markers were used: expressed sequence tag‐based simple sequence repeats and chloroplast DNA (cpDNA) sequence variations. Both sets of markers revealed clear genetic differentiation between populations in Borneo and those in the Malay Peninsula and Sumatra (Malay/Sumatra). However, in the south‐western part of Borneo, genetic admixture of the lineages was observed in the two marker types. Coalescent simulation based on cpDNA sequence variation suggested that the two lineages arose 0.28–0.09 million years before present and that following their divergence migration from Malay/Sumatra to Borneo strongly exceeded migration in the opposite direction. We conclude that the genetic structure of S. leprosula was largely formed during the middle Pleistocene and was subsequently modified by eastward migration across the subaerially exposed Sunda Shelf.     

Effects of Alkalinization and ATPase Inhibition on Stromal Free Mg2+ Concentration in Spinach Chloroplasts

Our earlier studies indicate that stromal alkalinization is essential for light-induced increase in free Mg²⁺ concentration ([Mg²⁺]) in chloroplast. Stromal [Mg²⁺] was increased by dark incubation of chloroplasts in the K⁺-gluconate medium (pH 8.0), or by NH₄Cl. These results indicate that stromal alkalinization can induce an increase in stromal [Mg²⁺] without illumination. Some inhibitors of envelope proton-translocating ATPase activity involved in H⁺ efflux inhibited the alkalinization-induced increase in [Mg²⁺].     

Studies on the Degradation Mechanisms of Proteins and their Derivatives in the Foods

The volatile sulfur components produced by boiling soybean meal hydrolyzates (AMINOSAN-EKI) have been identified as dimethyl sulfide and hydrogen sulfide. No mercaptan or disulfides were detected.

The main precursor of dimethyl sulfide is supposed to be methionine methylsulfonium compound derived from methionine and pectin substances (–COOCH₃) during the hydrolysis of soybean meal by hydrochloric acid.     

Studies on γ-Radiolysis of Sulfur Containing Amino Acids

In connection with flavor deterioration accompanied by food irradiation, the effect of γ-irradiation on sulfoxide amino acids in air free aqueous system was investigated. The major radiolysis products from S-n-propyl-l-cysteine sulfoxide (PCSO) were alanine, cysteic acid, dipropyl disulfide, etc., and from S-allyl-l-cysteine sulfoxide (ACSO) were S-allyl-l-cysteine, cystine, cysteic acid, etc., which were isolated chromatographycally and identified by using IR and mass spectrometry. The sulfoxide in ACSO was more easily reduced to sulfide than that of in PCSO, and the bond of S-C (β-carbon in alanine moiety) in ACSO was difficult to cleave. These differences observed between PCSO and ACSO in the radiolysis products and their yields indicate that the radiolysis degradation is considerably influenced by the structure of alkyl group. From the experiments with N₂O or KBr addition during irradiation, principal roles of the active species in irradiated water in the degradation processes were partly elucidated.     

An Acid- and Heat-stable β-Fructofuranosidase from Corticium rolfsii

We reported previously that an ndhB gene disruptant, ΔndhB, had the same phenotype as wild-type tobacco plants under normal growth conditions. Two other groups have reported conflicting phenotypes with each other for ndhCKJ operon disruptants. Here, we generated two transformants in which the ndhCKJ operon was disrupted, and found that new transformants had the same phenotype as ΔndhB. After illumination with visible light, all ndh disruptants had higher levels of steady-state fluorescence than wild-type controls when measured under weak light, suggesting that reduction of the plastoquinone pool in ndh disruptants was greater than that in wild-type controls. The weak light itself could not reduce the plastoquinone much, so the reduction in the plastoquinone in the mutant was due to electron donation from stromal reductants generated during illumination with the strong light. These results supported the hypothesis that NAD(P)H dehydrogenase prevents overreduction in chloroplasts and suggested that chlororespiratory oxidase did not function under low light or in the dark.     

The Heterogeneity of the 7S Soybean Protein by Sepharose Gel Chromatography and Disc Gel Electrophoresis

Two kinds of N-acetylmuramidase, M-1 and M-2 enzymes, that were isolated from the cultural broth of Stm. globisporus 1829, were remarkably different in amino acid composition, immunological properties and modes of lytic action from each other. The M-1 enzyme was composed of 186 amino acid residues of which two moles were of half cystine, while the M-2 enzyme was composed of 99 amino acid residues with no cysteine. The hydrolyzing action of the M-2 enzyme was suppressed by the presence of an O-acetyl group on muramic acid residues in the peptidoglycan moiety, while that of the M-l enzyme was independent of the presence of O-acetyl groups. However, the hydrolyzing activity of both enzymes was enhanced when some muramic acid residues were substituted with stem peptides containing alanine, isoglutamine and lysine.