Peach fruit PpNAC1 activates PpFAD3-1 transcription to provide ω-3 fatty acids for the synthesis of short-chain flavor volatiles

Multi-omics analysis unravels chemical roadmap and genetic basis for peach fruit aroma improvement

Selection of fruits with enhanced health benefits and superior flavor is an important aspect of peach breeding. Understanding the genetic interplay between appearance and flavor chemicals remains a major challenge. We identify the most important volatiles contributing to consumer preferences for peach, thus establishing priorities for improving flavor quality. We quantify volatiles of a peach population consisting of 184 accessions and demonstrate major reductions in the important flavor volatiles linalool and Z-3-hexenyl acetate in red-fleshed accessions. We identify 474 functional gene regulatory networks (GRNs), among which GRN05 plays a crucial role in controlling both red flesh and volatile content through the NAM/ATAF1/2/CUC (NAC) transcription factor PpBL. Overexpressing PpBL results in reduced expression of PpNAC1, a positive regulator for Z-3-hexenyl acetate and linalool synthesis. Additionally, we identify haplotypes for three tandem PpAATs that are significantly correlated with reduced gene expression and ester content. We develop genetic resources for improvement of fruit quality.

Multiple transcription factors of Arabidopsis thaliana that are activated by LEAFY COTYLEDON 2 regulate triacylglycerol biosynthesis

Plant triacylglycerols (TAG) are used in food and various industrial feedstocks. LEAFY COTYLEDON 2 (LEC2), a master positive regulator of TAG biosynthesis, regulates a complex network of transcription factors (TFs) during seed development. Aside from WRINKLED1 (WRI1), the TFs regulated by LEC2 related to TAG biosynthesis have not yet been identified. Previously, we identified 25 seed-expressing TFs that were upregulated in Arabidopsis leaves that overexpressed senescence-induced LEC2. In this study, each of the 25 TFs was transiently expressed in the leaves of Nicotiana benthamiana to identify unknown TFs that regulate TAG biosynthesis. The TAG content of the transformed leaves was analyzed using thin layer chromatography and gas chromatography. We observed that five TFs, ARABIDOPSIS RESPONSIVE REGULATOR 21 (ARR21), AINTEGUMENTA-LIKE 6 (AIL6), APETALA2/ETHYLENE RESPONSIVE FACTOR 55 (ERF55), WRKY DNA-BINDING PROTEIN 8 (WRKY8), and ARABIDOPSIS NAC DOMAIN CONTAINING PROTEIN 38 (ANAC038) increased TAG synthesis in the leaves. Among these, the promoters of AIL6, ERF55, WRKY8, and ANAC038 contain RY motifs, which are LEC2-binding sites activated by LEC2. AIL6 overexpression in Arabidopsis increased the total fatty acid (FA) content in seeds and altered the FA composition, with increases in 16:0, 18:1, and 18:2 and decreases in 18:0, 18:3, and 20:1 compared with those in the wild type (WT). AIL6 overexpression activates several FA and TAG biosynthesis genes. Therefore, our study successfully identified several new TFs regulated by LEC2 in TAG biosynthesis and showed that AIL6 increased the TAG content in seeds.

Tandem transcription factors PpNAC1 and PpNAC5 synergistically activate the transcription of the PpPGF to regulate peach softening during fruit ripening

Peach fruit rapidly soften after harvest, a significant challenge for producers and marketers as it results in rotting fruit and significantly reduces shelf life. In this study, we identified two tandem genes, PpNAC1 and PpNAC5, within the sr (slow ripening) locus. Phylogenetic analysis showed that NAC1 and NAC5 are highly conserved in dicots and that PpNAC1 is the orthologous gene of Non-ripening (NOR) in tomato. PpNAC1 and PpNAC5 were highly expressed in peach fruit, with their transcript levels up-regulated at the onset of ripening. Yeast two-hybrid and bimolecular fluorescence complementation assays showed PpNAC1 interacting with PpNAC5 and this interaction occurs with the tomato and apple orthologues. Transient gene silencing experiments showed that PpNAC1 and PpNAC5 positively regulate peach fruit softening. Yeast one-hybrid and dual luciferase assays and LUC bioluminescence imaging proved that PpNAC1 and PpNAC5 directly bind to the PpPGF promoter and activate its transcription. Co-expression of PpNAC1 and PpNAC5 showed higher levels of PpPGF activation than expression of PpNAC1 or PpNAC5 alone. In summary, our findings demonstrate that the tandem transcription factors PpNAC1 and PpNAC5 synergistically activate the transcription of PpPGF to regulate fruit softening during peach fruit ripening.

Transcription factor PpNAC1 and DNA demethylase PpDML1 synergistically regulate peach fruit ripening

Fruit ripening is accompanied by dramatic changes in color, texture, and flavor and is regulated by transcription factors (TFs) and epigenetic factors. However, the detailed regulatory mechanism remains unclear. Gene expression patterns suggest that PpNAC1 (NAM/ATAF1/2/CUC) TF plays a major role in peach (Prunus persica) fruit ripening. DNA affinity purification (DAP)-seq combined with transactivation tests demonstrated that PpNAC1 can directly activate the expression of multiple ripening-related genes, including ACC synthase1 (PpACS1) and ACC oxidase1 (PpACO1) involved in ethylene biosynthesis, pectinesterase1 (PpPME1), pectate lyase1 (PpPL1), and polygalacturonase1 (PpPG1) related to cell wall modification, and lipase1 (PpLIP1), fatty acid desaturase (PpFAD3-1), and alcohol acyltransferase1 (PpAAT1) involved in volatiles synthesis. Overexpression of PpNAC1 in the tomato (Solanum lycopersicum) nor (nonripening) mutant restored fruit ripening, and its transient overexpression in peach fruit induced target gene expression, supporting a positive role of PpNAC1 in fruit ripening. The enhanced transcript levels of PpNAC1 and its target genes were associated with decreases in their promoter mCG methylation during ripening. Declining DNA methylation was negatively associated with increased transcripts of DNA demethylase1 (PpDML1), whose promoter is recognized and activated by PpNAC1. We propose that decreased methylation of the promoter region of PpNAC1 leads to a subsequent decrease in DNA methylation levels and enhanced transcription of ripening-related genes. These results indicate that positive feedback between PpNAC1 and PpDML1 plays an important role in directly regulating expression of multiple genes required for peach ripening and quality formation.

Advancing tree genomics to future proof next generation orchard production

The challenges facing tree orchard production in the coming years will be largely driven by changes in the climate affecting the sustainability of farming practices in specific geographical regions. Identifying key traits that enable tree crops to modify their growth to varying environmental conditions and taking advantage of new crop improvement opportunities and technologies will ensure the tree crop industry remains viable and profitable into the future. In this review article we 1) outline climate and sustainability challenges relevant to horticultural tree crop industries, 2) describe key tree crop traits targeted for improvement in agroecosystem productivity and resilience to environmental change, and 3) discuss existing and emerging genomic technologies that provide opportunities for industries to future proof the next generation of orchards.

Integrated metabolomic and transcriptomic analyses revealed metabolite variations and regulatory networks in Cinnamomum cassia Presl from four growth years

To understand the mechanism of the dynamic accumulation of active ingredients in Cinnamomum cassia Presl, metabolomic and transcriptomic analyses of 5~8 years old C. cassia were performed. A total of 72 phenylpropanoids, 146 flavonoids, and 130 terpenoids showed marked changes. Most phenylpropanoids and flavonoids showed markedly higher abundances in 6-year-old C. cassia than in others, which was related to the higher expression of genes that synthesize and regulate phenylpropanoids and flavonoid. We identified transcription factors (TFs) and genes involved in phenylpropanoids and flavonoids synthesis and regulation through co-expression network analyses. Furthermore, most of the terpenoids in 5-year-old C. cassia showed markedly higher abundances than in others, which was due to the differentially expressed genes upstream of the terpenoids pathway. The results of our study provide new insights into the synthesis and accumulation of phenylpropanoid, flavonoids and terpenoids in C. cassia at four growth stages.

Progress and prospect: Biosynthesis of plant natural products based on plant chassis

Plant-derived natural products are a specific class of active substances with numerous applications in the medical, energy, and industrial fields. Many of these substances are in high demand and have become the fundamental materials for various purposes. Recently, the use of synthetic biology to produce plant-derived natural products has become a significant trend. Plant chassis, in particular, offer unique advantages over microbial chassis in terms of cell structure, product affinity, safety, and storage. The development of the plant hairy root tissue culture system has accelerated the commercialization and industrialization of synthetic biology in the production of plant-derived natural products. This paper will present recent progress in the synthesis of various plant natural products using plant chassis, organized by the types of different structures. Additionally, we will summarize the four primary types of plant chassis used for synthesizing natural products from plant sources and review the enabling technologies that have contributed to the development of synthetic biology in recent years. Finally, we will present the role of isolated and combined use of different optimization strategies in breaking the upper limit of natural product production in plant chassis. This review aims to provide practical references for synthetic biologists and highlight the great commercial potential of plant chassis biosynthesis, such as hairy roots.

Transcription factors MdMYC2 and MdMYB85 interact with ester aroma synthesis gene MdAAT1 in apple

Volatile esters in apple (Malus domestica) fruit are the critical aroma components determining apple flavor quality. While the exact molecular regulatory mechanism remains unknown, jasmonic acid (JA) plays a crucial role in stimulating the synthesis of ester aromas in apples. In our study, we investigated the effects of methyl jasmonate (MeJA) on the production of ester aroma in apples. MeJA treatment significantly increased ester aroma synthesis, accompanied by the upregulation of several genes involved in the jasmonate pathway transduction. Specifically, expression of the gene MdMYC2, which encodes a transcription factor associated with the jasmonate pathway, and the R2R3-MYB transcription factor gene MdMYB85 increased upon MeJA treatment. Furthermore, the essential gene ALCOHOL ACYLTRANSFERASE 1 (MdAAT1), encoding an enzyme responsible for ester aroma synthesis, showed increased expression levels as well. Our investigation revealed that MdMYC2 and MdMYB85 directly interacted with the promoter region of MdAAT1, thereby enhancing its transcriptional activity. In addition, MdMYC2 and MdMYB85 directly bind their promoters and activate transcription. Notably, the interaction between MdMYC2 and MdMYB85 proteins further amplified the regulatory effect of MdMYB85 on MdMYC2 and MdAAT1, as well as that of MdMYC2 on MdMYB85 and MdAAT1. Collectively, our findings elucidate the role of the gene module consisting of MdMYC2, MdMYB85, and MdAAT1 in mediating the effects of JA and promoting ester aroma synthesis in apples.

Analysis of Important Volatile Organic Compounds and Genes Produced by Aroma of Pepper Fruit by HS-SPME-GC/MS and RNA Sequencing

Pepper is an important condiment, and its aroma affects its commercial value. In this study, transcriptome sequencing and combined headspace solid-phase microextraction and gas chromatography-mass spectrometry (HS-SPME-GC-MS) were used to analyze the differentially expressed genes and volatile organic compounds in spicy and non-spicy pepper fruits. Compared with non-spicy fruits, there were 27 up-regulated volatile organic compounds (VOCs) and 3353 up-regulated genes (Up-DEGs) in spicy fruits. The results of KEGG enrichment analysis of the Up-DEGs combined with differential VOCs analysis showed that fatty acid biosynthesis and terpenoid biosynthesis may be the main metabolic pathways for aroma differences between non-spicy and spicy pepper fruits. The expression levels of the fatty acid biosynthesis-related genes FAD, LOX1, LOX5, HPL, and ADH and the key terpene synthesis gene TPS in spicy pepper fruits were significantly higher than those in non-spicy pepper fruits. The differential expression of these genes may be the reason for the different aroma. The results can provide reference for the development and utilization of high-aroma pepper germplasm resources and the breeding of new varieties.

Recent Advances in Research into Jasmonate Biosynthesis and Signaling Pathways in Agricultural Crops and Products

Jasmonates (JAs) are phospholipid-derived hormones that regulate plant development and responses to environmental stress. The synthesis of JAs and the transduction of their signaling pathways are precisely regulated at multiple levels within and outside the nucleus as a result of a combination of genetic and epigenetic regulation. In this review, we focus on recent advances in the regulation of JA biosynthesis and their signaling pathways. The biosynthesis of JAs was found to be regulated with an autocatalytic amplification mechanism via the MYC2 regulation pathway and inhibited by an autonomous braking mechanism via the MYC2-targeting bHLH1 protein to terminate JA signals in a highly ordered manner. The biological functions of JAs mainly include the promotion of fruit ripening at the initial stage via ethylene-dependent and independent ways, the regulation of mature coloring via regulating the degradation of chlorophyll and the metabolism of anthocyanin, and the improvement of aroma components via the regulation of fatty acid and aldehyde alcohol metabolism in agricultural crops. JA signaling pathways also function in the enhancement of biotic and abiotic stress resistance via the regulation of secondary metabolism and the redox system, and they relieve cold damage to crops through improving the stability of the cell membrane. These recently published findings indicate that JAs are an important class of plant hormones necessary for regulating plant growth and development, ripening, and the resistance to stress in agricultural crops and products.