Comparative Metabolites and Citrate-Degrading Enzymes Activities in Citrus Fruits Reveal the Role of Balance between ACL and Cyt-ACO in Metabolite Conversions

New Insights into the Genetic Basis of Lysine Accumulation in Rice Revealed by Multi-Model GWAS

Lysine is an essential amino acid that cannot be synthesized in humans. Rice is a global staple food for humans but has a rather low lysine content. Identification of the quantitative trait nucleotides (QTNs) and genes underlying lysine content is crucial to increase lysine accumulation. In this study, five grain and three leaf lysine content datasets and 4,630,367 single nucleotide polymorphisms (SNPs) of 387 rice accessions were used to perform a genome-wide association study (GWAS) by ten statistical models. A total of 248 and 71 common QTNs associated with grain/leaf lysine content were identified. The accuracy of genomic selection/prediction RR-BLUP models was up to 0.85, and the significant correlation between the number of favorable alleles per accession and lysine content was up to 0.71, which validated the reliability and additive effects of these QTNs. Several key genes were uncovered for fine-tuning lysine accumulation. Additionally, 20 and 30 QTN-by-environment interactions (QEIs) were detected in grains/leaves. The QEI-sf0111954416 candidate gene LOC_Os01g21380 putatively accounted for gene-by-environment interaction was identified in grains. These findings suggested the application of multi-model GWAS facilitates a better understanding of lysine accumulation in rice. The identified QTNs and genes hold the potential for lysine-rich rice with a normal phenotype.

Exogenous salicylic acid regulates organic acids metabolism in postharvest blueberry fruit

Fruit acidity is an essential factor affecting blueberry organoleptic quality. The organic acid content in blueberry fruit mainly contributes to fruit acidity. This study aims to evaluate the effect of exogenous salicylic acid (SA), the principal metabolite of aspirin, on the organoleptic quality and organic acid metabolism in rabbiteye blueberry (Vaccinium virgatum Ait, 'Powderblue') during cold storage (4 °C). Results showed that SA-treated fruit reduced fruit decay and weight loss delayed fruit softening, and decline of total soluble solids (TSS). TA and total organic acid amounts stayed the same during the late storage period in SA-treated fruit. Four kinds of organic acid components, malic acid, quinic acid, citric acid, and succinic acid, were at higher levels in fruit treated by SA as compared to control. SA enhanced the activities of PEPC, NAD-MDH, and CS to promote the synthesis of malic acid and citric acid. Meanwhile, the activities of NADP-ME, ACL, and ACO, which participated in the degradation of malic acid and citric acid, were inhibited by SA. qPCR results also showed that the expression of VcPEPC, VcNAD-MDH, and VcCS genes were upregulated. In contrast, SA downregulated the expression of VcNADP-ME, VcACL, and VcACO genes. In conclusion, SA could regulate the key genes and enzymes that participated in organic acids metabolism to maintain the freshness of blueberry during cold storage, therefore minimizing the economic loss.

Herbaceous peony PlACLB2 positively regulates red petal formation by promoting anthocyanin accumulation

ATP-citrate lyase (ACL) gene catalyzes the formation of acetyl-CoA to provide intermediate precursors for many secondary metabolites, and also plays an important role in anthocyanin biosynthesis of plants. Herbaceous peony (Paeonia lactiflora Pall.) is an international cut flower known for its rich flower colors, however, the function of the ACL gene in flower color regulation is still unclear. Here, double-colored P. lactiflora 'Hebao Jinlian' were used to study the molecular mechanism of red petal, and acetyl-CoA and anthocyanin biosynthesis related PlACLB2, PlCHS, PlDFR, PlANS, and PlbHLH1 genes were initially found to highly expressed in the red outer-petals. The expression pattern of PlACLB2 was consistent with the spatial accumulation of anthocyanins. The correlation analysis of PlACLB2 expression pattern, acetyl-CoA content, and anthocyanin accumulation revealed that PlACLB2 was positively correlated with the acetyl-CoA and anthocyanin contents with correlation coefficients of 0.82 and 0.80. Moreover, multiple sequence alignment identified two typical conserved domains in PlACLB2, and phylogenetic analysis clustered PlACLB2 into the ACLB clade. PlACLB2 was localized in the nucleus and cytoplasm. On the one hand, silencing PlACLB2 in P. lactiflora red outer-petal resulted in lighter petal color and decreased acetyl-CoA accumulation, and quantitative analysis detected that PlACLB2-silenced petals lost more anthocyanins than the control groups with a decrease of 31.0%, and the main pigment component cyanidin-3,5-O-diglucoside was reduced by 31.9%. On the other hand, overexpression of PlACLB2 significantly promoted red coloration, acetyl-CoA content, and anthocyanin accumulation in tobacco flowers. These results demonstrated that PlACLB2 promoted anthocyanin accumulation by increasing the abundance of its precursor substrate acetyl-CoA, thereby regulating the formation of the red petals in P. lactiflora.

Butyric and Citric Acids and Their Salts in Poultry Nutrition: Effects on Gut Health and Intestinal Microbiota

Intestinal dysfunction of farm animals, such as intestinal inflammation and altered gut microbiota, is the critical problem affecting animal welfare, performance and farm profitability. China has prohibited the use of antibiotics to improve feed efficiency and growth performance for farm animals, including poultry, in 2020. With the advantages of maintaining gut homeostasis, enhancing digestion, and absorption and modulating gut microbiota, organic acids are regarded as promising antibiotic alternatives. Butyric and citric acids as presentative organic acids positively impact growth performance, welfare, and intestinal health of livestock mainly by reducing pathogenic bacteria and maintaining the gastrointestinal tract (GIT) pH. This review summarizes the discovery of butyric acid (BA), citric acid (CA) and their salt forms, molecular structure and properties, metabolism, biological functions and their applications in poultry nutrition. The research findings about BA, CA and their salts on rats, pigs and humans are also briefly reviewed. Therefore, this review will fill the knowledge gaps of the scientific community and may be of great interest for poultry nutritionists, researchers and feed manufacturers about these two weak organic acids and their effects on intestinal health and gut microbiota community, with the hope of providing safe, healthy and nutrient-rich poultry products to consumers.

Profiling Analysis of Volatile and Non-volatile Compounds in Vitis Vinifera Berries (cv. Chardonnay) and Spontaneous Bud Mutation

A novel clonal variety of Vitis vinifera was identified from “Chardonnay” using inter-simple sequence repeat (ISSR) markers and called “bud mutation. ” The metabolomic profiles in Chardonnay and bud mutation berries indicated essential differences in the expression of key genes in the pathways of 2-C-methyl-D-erythritol-4-phosphate (MEP) and lipoxygenase-hydroperoxide lyase (LOX-HPL). Bud mutation fruits also matured 10 days earlier than Chardonnay and have higher carotenoid, sugar, and acidic compound contents. Furthermore, the gene expression was examined in the biosynthetic pathways of two ripening-associated hormones, abscisic acid (ABA) and jasmonic acid (JA), which significantly increased in bud mutation compared with the Chardonnay fruit. The synthesis and metabolism of amino acids, terpenes, fatty acids, volatile components, and specialized metabolites significantly increased in bud mutation. Therefore, in comparison with Chardonnay, bud mutation is considered a highly aroma-producing grape variety for an improvement in the beverage industry.

Multiomic Analysis Elucidates the Reasons Underlying the Differential Metabolite Accumulation in Citrus Mature Leaves and Fruit Juice Sacs

Fruit and leaf possess distinctly different metabolites. Here, metabolites and transcriptome were compared between mature leaves (ML) and juice sacs (JS) of Citrus grandis "Hirado Buntan" to investigate the possible reasons. Results indicated that the remarkable difference in starch, total flavonoids and carotenoids, l-ascorbate, and jasmonic acid between ML and JS was tightly related to the expression levels of their biosynthesis-related genes, while the significant difference in abscisic acid and citrate was mainly related to the gene expression level(s) of 9-cis-epoxycarotenoid dioxygenase and proton pump genes, respectively. In addition, ATP citrate lyase probably plays a key role in the levels of flavonoids between ML and JS via providing different levels of acetyl-CoA. Taken together, these results identified some key candidate genes responsible for the content of a given metabolite and will contribute to research in regulating such metabolite content in citrus fruits.