Arbuscular mycorrhizal fungi (AMF) typically exhibit reduced diversity in nutrient-rich soils. However, whether the influence of host plants on AMF within the rhizosphere is direct or indirect through the alteration of soil nutrient levels has yet to be determined. This study explored the diversity and colonization of AMF in the National Tropical Fruit Tree Genebank, where chemical fertilizers are used to preserve minor tropical fruit germplasms. We aimed to understand the direct and indirect effects of host plants on AMF community dynamics, sporulation, and colonization. By analyzing fine roots and rhizosphere soil from 12 tropical fruit trees, we assessed mycorrhizal colonization indices, soil nutrients, AMF spore density, and community structure. Despite their low colonization density and arbuscular abundance, all the tree roots harbored AMF, with spore densities ranging from 24.00 to 204.80 spores/100 g of dry soil. High-throughput sequencing identified 207 AMF virtual taxa (VTs) from 60 soil samples, with dominant taxa, including early-evolved Paraglomus fungi and ruderal AMF, being minimally affected by soil nutrient levels. Interestingly, there was no correlation between α diversity and spore density. Structural equation modeling (SEM) indicated that host plant evolutionary divergence time (ET) directly influenced AMF α diversity indices and indirectly impacted spore density via soil nutrients. However, neither ETs nor soil nutrients significantly affected the AMF community structure, with only arbuscular abundance showing a negative correlation with ET. This research underscores the intricate relationship between host plants and AMF in genebanks, offering insights for effective AMF resource management and informed conservation practices. Graphical Abstract

Harvesting fruits prematurely is a serious problem in many Camellia oleifera ‘Huaxin’ orchards. Systematic views of dynamic alterations in central metabolism associated with the oil content and oil quality of this cultivar at different harvesting dates were investigated. Oil trait analysis was performed in conjunction with data-independent acquisition proteomics analysis using kernels harvested at three time points. Samples were taken from different years and locations to verify oil trait changes, and parallel reaction monitoring (PRM) was performed for some pivotal proteins to validate changes in their abundance. Samples harvested at 6 days after the recommended harvesting date had the highest contents and best fatty acid composition of Camellia oil. A total of 614 differentially accumulated proteins were detected in three pairwise comparisons. Six days prior to the recommended harvesting date, maximum expression of ribonucloprotein, helicase ATP-binding domain-containing protein, and glycerol kinase and the highest seed moisture content were observed. Highest mitogen-activated protein kinase 6, very-long-chain 3-oxoacyl-CoA reductase and stearoyl-CoA desaturase expression appeared on the recommended harvesting date. A delayed effect was observed for proteomic and oil trait data. Oil trait and PRM validations indicated our results to be highly reliable. The current data strongly suggest that in Guizhou Province,’Huaxin’ cannot be harvested earlier than the recommended harvesting date; appropriately delaying the harvesting time can improve the ultimate production and quality of Camellia oil.

The regulatory network governing triacylglycerol (TAG) and fatty acid (FA) accumulation in hexaploid Camellia oleifera kernels remains unclear due to the lack of an appropriate reference genome. In this study, we combined oil trait measurements with multi-omics analyses (global transcriptomics, miRNA sequencing, proteomics, and metabolomics) across 3 harvest stages, using the hexaploid C. oleifera ‘Changlin 40’ genome as reference. Integrated analysis of oil traits and multi-omics data demonstrated that premature harvesting (1 week before the recommended date) decreased oil production and enhanced saturated FAs composition, while postponed harvesting (1 week after the recommended date) preserved oil yield and increased oleic and linolenic acid contents. Comprehensive pathway analysis identified 11 key metabolic pathways involved in TAG and FA biosynthesis and catabolism, revealing their coordination with terpene and flavonoid synthesis under the influence of carbohydrate metabolism. Within the 11 metabolic pathways, key regulatory enzymes comprised alcohol dehydrogenase and galactosidase that negatively regulated TAG biosynthesis, palmitoyl-protein thioesterase that mediated short-chain saturated FA formation, and acyl-CoA thioesterase that enhanced long-chain unsaturated FA production. Additionally, we detected novel associations between TAG/FA accumulation and non-canonical factors, including noncoding RNAs (circR007, lncR114741, miR167h, miR166, miR398a-3p, miR398d, and miR396a-3p), proteins (seed storage protein, caffeic acid O-methyltransferase, galactose oxidase, No Pollen Germination 1, Coronatine Insensitive 1), and metabolites (L-carnitine and L-glutamate). The reliability of our findings was confirmed through qRT-PCR (RNA validation) and Parallel Reaction Monitoring (protein validation). This study established the regulatory network TAG and FA accumulation in hexaploid C. oleifera kernels, and provided foundational molecular framework for breeding high-yield, high-quality C. oleifera cultivars through marker-assisted selection.