Light induces gene expression to enhance the synthesis of storage reserves in Brassica napus L. embryos

Genome-wide identification and mining elite allele variation of the Monoacylglycerol lipase (MAGL) gene family in upland cotton (Gossypium hirsutum L.)

BACKGROUND

Monoacylglycerol lipase (MAGL) genes belong to the alpha/beta hydrolase superfamily, catalyze the terminal step of triglyceride (TAG) hydrolysis, converting monoacylglycerol (MAG) into free fatty acids and glycerol.

RESULTS

In this study, 30 MAGL genes in upland cotton have been identified, which have been classified into eight subgroups. The duplication of GhMAGL genes in upland cotton was predominantly influenced by segmental duplication events, as revealed through synteny analysis. Furthermore, all GhMAGL genes were found to contain light-responsive elements. Through comprehensive association and haplotype analyses using resequencing data from 355 cotton accessions, GhMAGL3 and GhMAGL6 were detected as key genes related to lipid hydrolysis processes, suggesting a negative regulatory effect.

CONCLUSIONS

In summary, MAGL has never been studied in upland cotton previously. This study provides the genetic mechanism foundation for the discover of new genes involved in lipid metabolism to improve cottonseed oil content, which will provide a strategic avenue for marker-assisted breeding aimed at incorporating desirable traits into cultivated cotton varieties.

Genome-Wide Analysis and Functional Characterization of LACS Gene Family Associated with Lipid Synthesis in Cotton (Gossypium spp.)

Cotton (Gossypium spp.) is the fifth largest oil crop in the world, and cottonseed provides abundant vegetable oil resources and industrial bioenergy fuels for people; therefore, it is of practical significance to increase the oil content of cotton seeds for improving the oil yield and economic benefits of planting cotton. Long-chain acyl-coenzyme A (CoA) synthetase (LACS) capable of catalyzing the formation of acyl-CoAs from free fatty acids has been proven to significantly participate in lipid metabolism, of which whole-genome identification and functional characterization of the gene family have not yet been comprehensively analyzed in cotton. In this study, a total of sixty-five LACS genes were confirmed in two diploid and two tetraploid Gossypium species, which were divided into six subgroups based on phylogenetic relationships with twenty-one other plants. An analysis of protein motif and genomic organizations displayed structural and functional conservation within the same group but diverged among the different group. Gene duplication relationship analysis illustrates the LACS gene family in large scale expansion through WGDs/segmental duplications. The overall Ka/Ks ratio indicated the intense purifying selection of LACS genes in four cotton species during evolution. The LACS genes promoter elements contain numerous light response cis-elements associated with fatty acids synthesis and catabolism. In addition, the expression of almost all GhLACS genes in high seed oil were higher compared to those in low seed oil. We proposed LACS gene models and shed light on their functional roles in lipid metabolism, demonstrating their engineering potential for modulating TAG synthesis in cotton, and the genetic engineering of cottonseed oil provides a theoretical basis.

Transcriptomic comparison of seeds and silique walls from two rapeseed genotypes with contrasting seed oil content

Silique walls play pivotal roles in contributing photoassimilates and nutrients to fuel seed growth. However, the interaction between seeds and silique walls impacting oil biosynthesis is not clear during silique development. Changes in sugar, fatty acid and gene expression during Brassica napus silique development of L192 with high oil content and A260 with low oil content were investigated to identify key factors affecting difference of their seed oil content. During the silique development, silique walls contained more hexose and less sucrose than seeds, and glucose and fructose contents in seeds and silique walls of L192 were higher than that of A260 at 15 DAF, and sucrose content in the silique walls of L192 were lower than that of A260 at three time points. Genes related to fatty acid biosynthesis were activated over time, and differences on fatty acid content between the two genotypes occurred after 25 DAF. Genes related to photosynthesis expressed more highly in silique walls than in contemporaneous seeds, and were inhibited over time. Gene set enrichment analysis suggested photosynthesis were activated in L192 at 25 and 35 DAF in silique walls and at both 15 and 35 DAF in the seed. Expressions of sugar transporter genes in L192 was higher than that in A260, especially at 35 DAF. Expressions of genes related to fatty acid biosynthesis, such as BCCP2s, bZIP67 and LEC1s were higher in L192 than in A260, especially at 35 DAF. Meanwhile, genes related to oil body proteins were expressed at much lower levels in L192 than in A260. According to the WGCNA results, hub modules, such as ME.turquoise relative to photosynthesis, ME.green relative to embryo development and ME.yellow relative to lipid biosynthesis, were identified and synergistically regulated seed development and oil accumulation. Our results are helpful for understanding the mechanism of oil accumulation of seeds in oilseed rape for seed oil content improvement.

Metabolite Characteristics Analysis of Siliques and Effects of Lights on the Accumulation of Glucosinolates in Siliques of Rapeseed

Glucosinolates (GSLs) are naturally occurring secondary metabolites found in the Brassicaceae family, which mainly synthesize in the siliques with a wide range of functions. In this study, we investigated the effects of lights on metabolites in siliques of rapeseed through ultra high-performance liquid chromatography (UPLC)-heated electrospray ionization (HESI)-tandem mass spectrometry (MS/MS). A total of 249 metabolites, including 29 phenolic acids, 38 flavonoids, 22 GSLs, 93 uncalculated and 67 unknown compounds, were identified in siliques of rapeseed. Meanwhile, 62 metabolites showed significant differences after shading treatment, which were mainly GSLs and unknown compounds. Interestingly, the amounts of 10 GSLs had high accumulation levels in siliques, while the expression levels of their corresponding biosynthetic genes (AOP, GSL-OH, IGMT, and ST5a) were obviously reduced after shading treatment. Further evidence showed that the amounts of GSLs were significantly reduced in seeds, in accordance with the expression profiles of transporter genes (BnaGTRs). Our findings indicated that lights could affect the accumulation and transportation of GSLs from siliques to seeds in rapeseed. Therefore, this study facilitates a better understanding of metabolic characteristics of siliques and provides insight into the importance of light for GSLs accumulation and transportation in siliques and seeds of rapeseed.

Triacylglycerol biosynthesis in shaded seeds of tung tree (Vernicia fordii) is regulated in part by Homeodomain Leucine Zipper 21

Light quantity and quality affect many aspects of plant growth and development. However, few reports have addressed the molecular connections between seed oil accumulation and light conditions, especially dense shade. Shade-avoiding plants can redirect plant resources into extension growth at the expense of leaf and root expansion in an attempt to reach areas containing richer light. Here, we report that tung tree seed oil accumulation is suppressed by dense shade during the rapid oil accumulation phase. Transcriptome analysis confirmed that oil accumulation suppression due to dense shade was attributed to reduced expression of fatty acid and triacylglycerol biosynthesis-related genes. Through weighted gene co-expression network analysis, we identified 32 core transcription factors (TFs) specifically upregulated in densely shaded seeds during the rapid oil accumulation period. Among these, VfHB21, a class I homeodomain leucine zipper TF, was shown to suppress expression of FAD2 and FADX, two key genes related to α-eleostearic acid, by directly binding to HD-ZIP I/II motifs in their respective promoter regions. VfHB21 also binds to similar motifs in the promoters of VfWRI1 and VfDGAT2, two additional key seed lipid regulatory/biosynthetic genes. Functional conservation of HB21 during plant evolution was demonstrated by the fact that AtWRI1, AtSAD1, and AtFAD2 were downregulated in VfHB21-overexpressor lines of transgenic Arabidopsis, with concomitant seed oil reduction, and the fact that AtHB21 expression also was induced by shade. This study reveals some of the regulatory mechanisms that specifically control tung tree seed oil biosynthesis and more broadly regulate plant storage carbon partitioning in response to dense shade conditions.