This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange–correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear–electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an “open teamware” model and an increasingly modular design.

We recently reported the cloning and characterization of an Arabidopsis (ecotype Columbia) diacylglycerol acyltransferase cDNA (Zou et al., 1999) and found that in Arabidopsis mutant line AS11, an ethyl methanesulfonate-induced mutation at a locus on chromosome II designated as Tag1 consists of a 147-bp insertion in the DNA, which results in a repeat of the 81-bp exon 2 in the Tag1 cDNA. This insertion mutation is correlated with an altered seed fatty acid composition, reduced diacylglycerol acyltransferase (DGAT; EC 2.3.1.20) activity, reduced seed triacylglycerol content, and delayed seed development in the AS11 mutant. The effect of the insertion mutation on microsomal acyl-coenzyme A-dependent DGAT is examined with respect to DGAT activity and its substrate specificity in the AS11 mutant relative to wild type. We demonstrate that transformation of mutant AS11 with a single copy of the wild-type Tag1 DGAT cDNA can complement the fatty acid and reduced oil phenotype of mutant AS11. More importantly, we show for the first time that seed-specific over-expression of the DGAT cDNA in wild-type Arabidopsis enhances oil deposition and average seed weight, which are correlated with DGAT transcript levels. The DGAT activity in developing seed of transgenic lines was enhanced by 10% to 70%. Thus, the current study confirms the important role of DGAT in regulating the quantity of seed triacylglycerols and the sink size in developing seeds.

In characterizing the enzymes involved in the formation of very long-chain fatty acids (VLCFAs) i n the Brassicaceae, we have generated a series of mutants of Arabidopsis thaliana that have reduced VLCFA content. Here we report the characterization of a seed lipid mutant, AS1 1, which, in comparison to wild type (WT), has reduced levels of 20:l and 18:l and accumulates 18:3 as the major fatty acid in triacylglycerols. Proportions of 18:2 remain similar to WT. Cenetic analyses indicate that the fatty acid phenotype is caused by a semidominant mutation in a single nuclear gene, designated TAC1, located on chromosome 2. Biochemical analyses have shown that the AS11 phenotype is not due to a deficiency in the capacity t o elongate 18:l or to an increase in the relative A1 5 or A1 2 desaturase activities. Indeed, the ratio of desaturase/elongase activities measured in vitro is virtually identical in developing WT and AS1 1 seed homogenates. Rather, the fatty acid phenotype of AS1 1 is the result of reduced diacylglycerol acyltransferase activity throughout development, such that triacylglycerol biosynthesis is reduced. This leads to a reduction in 20:l biosynthesis during seed development, leaving more 18:l available for desaturation. Thus, we have demonstrated that changes to triacylglycerol biosynthesis can result i n dramatic changes i n fatty acid composition and, in particular, i n the accumulation of VLCFAs i n seed storage lipids.The fatty acyl composition of seed TAGs determines their physical and chemical properties and, thus, their use in edible oil or industrial applications. TAG composition depends on the interaction of several different groups of enzymes in the lipid biosynthesis pathway. The enzymes of the fatty acid synthase complex in the plastids of developing seeds are responsible for the biosynthesis of fatty acids up to and including oleic acid. Modifying enzymes, such as the extraplastidic A12 and A15 desaturases, elongases, hydroxylases, and epoxidases, yield polyunsaturated, very long-chain, hydroxy-, and epoxy-fatty acids, respectively. Acyltransferases insert specific acyl moieties onto the glyc-

A putative yeast sn-2 acyltransferase gene (SLC7-7), reportedly a variant acyltransferase that suppresses a genetic defect in sphingolipid long-chain base biosynthesis, has been expressed in a yeast SLC deletion strain. The SLC7-7 gene product was shown in vitro to encode an sn-2 acyltransferase capable of acylating sn-1 oleoyl-lysophosphatidic acid, using a range of acyl-COA thioesters, including 181-, 22:l-, and 240-COAS. The SLC7-7 gene was introduced into Arabidopsis and a high erucic acid-containing Brassica napus cv Hero under the control of a constitutive (tandem cauliflower mosaic virus 35s) promoter. The resulting transgenic plants showed substantial increases of 8 to 48% in seed oil content (expressed on the basis of seed dry weight) and increases in both overall proportions and amounts of very-long-chain fatty acids in seed triacylglycerols (TAGs). Furthermore, the proportion of very-long-chain fatty acids found at the sn-2 position of TAGs was increased, and homogenates prepared from developing seeds of transformed plants exhibited elevated lysophosphatidic acid acyltransferase (EC 2.3.1 51) activity. Thus, the yeast sn-2 acyltransferase has been shown to encode a protein that can exhibit lysophosphatidic acid acyltransferase activity and that can be used to change total fatty acid content and composition as well as to alter the stereospecific acyl distribution of fatty acids in seed TAGS.

SummaryA full-length cDNA encoding a putative diacylglycerol acyltransferase 1 (DGAT1, EC seed-specific expression of TmDGAT1 was able to complement the low TAG/unusual fatty acid phenotype of the Arabidopsis AS11 ( DGAT1 ) mutant. Over-expression of TmDGAT1 in wild-type Arabidopsis and high-erucic-acid rapeseed (HEAR) and canola Brassica napus resulted in an increase in oil content (3.5%-10% on a dry weight basis, or a net increase of 11%-30%). Site-directed mutagenesis was conducted on six putative functional regions/ motifs of the TmDGAT1 enzyme. Mutagenesis of a serine residue in a putative SnRK1 target site resulted in a 38%-80% increase in DGAT1 activity, and over-expression of the mutated TmDGAT1 in Arabidopsis resulted in a 20%-50% increase in oil content on a per seed basis.Thus, alteration of this putative serine/threonine protein kinase site can be exploited to enhance DGAT1 activity, and expression of mutated DGAT1 can be used to enhance oil content.