Genome-Wide Association Studies Provide Insights into the Genetic Determination of Flower and Leaf Traits of Actinidia eriantha

Transcriptome-Wide Association Analysis of Flavonoid Biosynthesis Genes and Their Correlation With Leaf Phenotypes in Hawk Tea (Litsea coreana var. sinensis)

Hawk tea (Litsea coreana var. sinensis), derived from the tender shoots or leaves, rich in flavonoids can promote healthcare for humans. The primary flavonoid are kaempferol-3-O-β-D-glucoside, kaempferol-3-O-β-D-galactoside, quercetin-3-O-β-D-glucoside, and quercetin-3-O-β-D-galactoside. The existence of an association between leaf phenotype and flavonoid content, along with the underlying mechanisms of flavonoid biosynthesis, remains incompletely understood. In this study, 109 samples were analyzed to determine the correlation and genetic variability in leaf phenotype and flavonoid content. Furthermore, a transcriptome-wide association study identified candidate loci implicated in the biosynthesis of four key flavonoids. The study revealed that genetic variability in leaf traits and flavonoid concentrations is predominantly attributed to interpopulation differences. Flavonoid accumulation was significantly correlated with tree DBH, indicative of age-related traits. Transcriptome-wide association analysis identified 84 significant SNPs associated with flavonoid content, with only 13 located within gene regions. The majority of these genes are implicated in metabolic processes and secondary metabolite biosynthesis. Notably, structural genes within these regions are directly involved in pathways known to regulate flavonoid metabolism, exerting a pivotal influence on flavonoid biosynthesis. These results revealed the physiological basis for the regulation of flavonoid content, as well as the molecular mechanisms for the biosynthesis of flavonoids in hawk tea. It also lays theoretical groundwork for subsequent explorations into the genetic determinants influencing flavonoid accumulation of hawk tea.

L-Ascorbic acid metabolism and regulation in fruit crops

L-Ascorbic acid (AsA) is more commonly known as vitamin C and is an indispensable compound for human health. As a major antioxidant, AsA not only maintains redox balance and resists biological and abiotic stress but also regulates plant growth, induces flowering, and delays senescence through complex signal transduction networks. However, AsA content varies greatly in horticultural crops, especially in fruit crops. The AsA content of the highest species is approximately 1,800 times higher than that of the lowest species. There have been significant advancements in the understanding of AsA accumulation in the past 20 years. The most noteworthy accomplishment was the identification of the critical rate-limiting genes for the 2 major AsA synthesis pathways (L-galactose pathway and D-galacturonic acid pathway) in fruit crops. The rate-limiting genes of the former are GMP, GME, GGP, and GPP, and the rate-limiting gene of the latter is GalUR. Moreover, APX, MDHAR, and DHAR are also regarded as key genes in degradation and regeneration pathways. Interestingly, some of these key genes are sensitive to environmental factors, such as GGP being induced by light. The efficiency of enhancing AsA content is high by editing upstream open reading frames (uORF) of the key genes and constructing multi-gene expression vectors. In summary, the AsA metabolism has been well understood in fruit crops, but the transport mechanism of AsA and the synergistic improvement of AsA and other traits is less known, which will be the focus of AsA research in fruit crops.