The Serine Carboxypeptidase-Like Gene SCPL41 Negatively Regulates Membrane Lipid Metabolism in Arabidopsis thaliana

The Arabidopsis has 51 proteins annotated as serine carboxypeptidase-like (SCPL) enzymes. Although biochemical and cellular characterization indicates SCPLs involved in protein turnover or processing, little is known about their roles in plant metabolism. In this study, we identified an Arabidopsis mutant, bis4 (1-butanol insensitive 4), that was insensitive to the inhibitory effect of 1-butanol on seed germination. We cloned the gene that was defective in bis4 and found that it encoded an SCPL41 protein. Transgenic Arabidopsis plants constitutively expressing SCPL41 were generated, oil body staining and lipidomic assays indicated that SCPL41-overexpressing plants showed a decrease in membrane lipid content, especially digalactosyl diglyceride (DGDG) and monogalactosyl diglyceride (MGDG) contents, while the loss of SCPL41 increased the membrane lipid levels compared with those in wild-type plants. These findings suggested that SCPL41 had acquired novel functions in membrane lipid metabolism.

Structure of the plant photosystem I

Plant photosystem I (PSI) is one of the most intricate membrane complexes in nature. It comprises two complexes, a reaction center and light-harvesting complex (LHC), which together form the PSI–LHC supercomplex. The crystal structure of plant PSI was solved with two distinct crystal forms. The first, crystallized at pH 6.5, exhibited P21 symmetry; the second, crystallized at pH 8.5, exhibited P212121 symmetry. The surfaces involved in binding plastocyanin and ferredoxin are identical in both forms. The crystal structure at 2.6 Å resolution revealed 16 subunits, 45 transmembrane helices, and 232 prosthetic groups, including 143 chlorophyll a, 13 chlorophyll b, 27 β-carotene, 7 lutein, 2 xanthophyll, 1 zeaxanthin, 20 monogalactosyl diglyceride, 7 phosphatidyl diglyceride, 5 digalactosyl diglyceride, 2 calcium ions, 2 phylloquinone, and 3 iron sulfur clusters. The model reveals detailed interactions, providing mechanisms for excitation energy transfer and its modulation in one of nature's most efficient photochemical machine.

Brachybacterium saurashtrense sp. nov., a halotolerant root-associated bacterium with plant growth-promoting potential

A Gram-positive-staining, aerobic, non-motile, coccoid shaped, halotolerant bacterium (strain JG 06T) was isolated from the roots of Salicornia brachiata, an extreme halophyte. Phylogenetic analysis based on 16S rRNA gene sequence showed that the novel strain had sequence similarities of 99.2 % to Brachybacterium paraconglomeratum JCM 11608T, 99.0 % to Brachybacterium conglomeratum DSM 10241 and 98.2 % to Brachybacterium faecium DSM 4810T. DNA–DNA hybridization with B. paraconglomeratum DSM 46341T, B. conglomeratum DSM 10241T, B. faecium DSM 4810T, Brachybacterium tyrofermentans DSM 10673T, Brachybacterium alimentarium DSM 10672T, Brachybacterium fresconsis DSM 14564T, Brachybacterium sacelli DSM 14566T and Brachybacterium muris DSM 15460T resulted in reassociation values of 36.2 %, 36.5 %, 35.8 %, 27.6 %, 27.9 %, 28.2 %, 28.7 % and 11.2 %, respectively. The peptidoglycan type of strain JG 06T was variant A4γ. The menaquinone content was MK7 (100 %). The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, monogalactosyl diglyceride, three unidentified phospholipids and three glycolipids. The predominant fatty acid was anteiso-C15 : 0 (52.07 %); significant amounts of iso-C16 : 0 (12.38 %), iso-C15 : 0 (8.59 %) and anteiso-C17 : 0 (10.03 %) were also present. The G+C content of the DNA was 73.0 mol%. The strain formed a growth pellicle in nitrogen-free semisolid NFb medium containing NaCl at levels of up to 4 % (w/v) and reduced acetylene to ethylene, a result indicative of N2 fixation. In nutrient broth medium the novel strain grew at NaCl concentrations up to 15 % (w/v). It also had the ability to produce indole-3-acetic acid (IAA) and siderophores, utilized 1-aminocyclopropane-1-carboxylate (ACC) as a sole source of nitrogen and possessed the ACC deaminase enzyme. On the basis of physiological, biochemical data and phylogenetic analyses, strain JG 06T should be placed in the genus Brachybacterium. Strain JG 06T represents a novel species of the genus Brachybacterium for which the name Brachybacterium saurashtrense sp. nov. is proposed (type strain JG 06T = DSM 23186T = IMCC 252T).

(250) Monogalactosyl-diglyceride Contents in Sweetpotato Clones

Bioasssay-guided investigation of constituents possibly contributing to the allelopathic potential of sweetpotato led to the isolation of a nonpolar seed germination inhibitor in sweetpotato (Ipomoea batatas L.) roots. Mass spectral data supported by HPLC s pectroscopic analyses and data obtained from hydrolysis products revealed the presence of three monogalactosyl-diglycerides (MGDGs) (galactosyl-di-linoleneoyl glyceride, galactosyl-linoleneoyl-linoleoyl glyceride, and galactosyl-di-linoleoyl glyceride) in storage roots. The compounds inhibited proso millet germination, and at 100 ppm inhibition was about 90%. MGDG with fully saturated fatty acids (galactosyl-distearoyl glyceride) was not inhibitory in the bioassay. An efficient method for quantitation of individual MGDGs was developed, and the contents of each compound in the storage root tissues of 12 genetically diverse cultivars and breeding lines were determined. On a dry weight basis, total MGDG contents ranged between 107 and 452 μg/g in the periderm, 298 and 807 μg/g in the cortex, and 296 and 755 μg/g in the stele. Also, large differences in the ratios of the three compounds between clones and between tissues within a clone were noted. The differences between clones indicate that manipulating total content and ratios of MGDGs through plant breeding is feasible.