Chromosome-scale genome assembly and population genomics provide insights into the adaptation, domestication, and flavonoid metabolism of Chinese plum.

Globally, commercialized plum cultivars are mostly diploid Chinese plums (Prunus salicina Lindl.), also known as Japanese plums, and are one of the most abundant and variable fruit tree species. To advance Prunus genomic research, we present a chromosome-scale P. salicina genome assembly, constructed using an integrated strategy that combines Illumina, Oxford Nanopore, and high-throughput chromosome conformation capture (Hi-C) sequencing. The high-quality genome assembly consists of a 318.6-Mb sequence (contig N50 length of 2.3 Mb) with eight pseudo-chromosomes. The expansion of the P. salicina genome is led by recent segmental duplications and a long terminal repeat burst of approximately 0.2 Mya. This resulted in a significant expansion of gene families associated with flavonoid metabolism and plant resistance, which impacted fruit flavor and increased species adaptability. Population structure and domestication history suggest that Chinese plum may have originated from South China and provides a domestication route with accompanying genomic variations. Selection sweep and genetic diversity analysis enabled the identification of several critical genes associated with flowering time, stress tolerance, and flavonoid metabolism, demonstrating the essential roles of related pathways during domestication. Furthermore, we reconstructed and exploited flavonoid-anthocyanin metabolism using multi-omics analysis in Chinese plum and proposed a complete metabolic pathway. Collectively, our results will facilitate further candidate gene discovery for important agronomic traits in Chinese plum and provide insights into future functional genomic studies and DNA-informed breeding.

Biostimulants promote the accumulation of carbohydrates and biosynthesis of anthocyanins in 'Yinhongli' plum.

Biostimulants play an important role in promoting crop growth and development and improving fruit yield, but their influence on fruit quality in horticulture plants is still unclear. In this study, four types of biostimulants, Ainuo (AN), Aigefu (AG), Weiguo (WG), and Guanwu Shuang (GS) were applied to the fruit surface of 'Yinhongli' plum at 60 and 75 days after anthesis to investigate their effect on carbohydrates and biosynthesis of anthocyanins, and also analyze the relationship between sugar and anthocyanin accumulation during fruit color change to ripening. Results showed that all biostimulant treatments significantly improved fruit appearance quality, and increased single fruit weight and TSS/TA. Cyanidin 3-O-glucoside and cyanidin 3-O-rutinoside, are the most important anthocyanins in the red skin of the 'Yinhongli' plum, and no anthocyanin was detected in the green skin. In addition, WG and GS treatments significantly increased the expression of structural genes involved in anthocyanin biosynthesis compared with the control, especially chalcone synthase (CHS) and flavonoid 3-O-glucosyltransferase (UFGT) at 95-105 d after anthesis, leading to anthocyanin accumulation 10 days earlier than the control. Correlation analysis showed that there was a significant correlation between total sugar and anthocyanin content during fruit coloring and ripening.

Japanese plums behavior under water stress: impact on yield and biochemical traits.

This work investigates response to drought of nine local cultivars alongside two exotic varieties of Japanese plum (Prunus salicina L.) through their yield and fruit quality components. It was carried out at Sais plain, northern Morocco, over two consecutive years (2019-2020). Water stress was imposed by a deficit irrigation (DI) treatment of 50% ETc during the whole fruit growth period, compared to full irrigation of 100% ETc (CI). At their full ripening stage, the cultivars were assessed for their yield, fruit weight and fruit quality attributes, namely total soluble solids (TSS), pH, titratable acidity (TA), maturity index (MI), soluble sugars content (SSC), amino acids content (AAC), total phenolic compounds (TPC) and total antioxidant capacity (TAC). Results displayed significant decrease in yield and fruit weight since the first year of DI application. Owing to calculated stability indexes of the aforementioned traits along with water use efficiency, the local cultivar 'Fortu-43' was the most insensitive to drought, whereas 'Timhdit' and 'Black-D35' showed the lowest drought tolerability. The effects of water stress on fruit chemical and biochemical traits varied significantly among cultivars, exhibiting an overall significant improvement in fruit quality. Two-dimensional clustered heatmap analysis subdivided the cultivars into two distinct clusters, mainly discriminated based on stability indexes of SSC, MI, TPC and TAC. Among the latter, SSC stability index was probably the most significant drought tolerance marker for Japanese plum.

Conjugated Polyamines in Root Plasma Membrane Enhanced the Tolerance of Plum Seedling to Osmotic Stress by Stabilizing Membrane Structure and Therefore Elevating H+-ATPase Activity.

Polyamines are small positively charged molecules in plants and play important functions in many biological processes under various environmental stresses. One of the most confounding problems relating to polyamines (PAs) in stresses is the lack of understanding of the mechanisms underlying their function(s). Furthermore, a limited number of studies have addressed this issue at the sub-cellular level, especially in tree plants under drought stress. Therefore, in this research, by simulating natural drought stress with polyethylene glycol (PEG) osmotic stress, the relationship between the levels of conjugated polyamines and the activity of H+-ATPase in the plasma membrane was elucidated with the roots of two plum (Prunus salicina L.) cultivars, which were different in drought tolerance, as experimental materials. Furthermore, free PA levels and the activities of S-adenosylmethionine decarboxylase (SAMDC) and transglutaminase (TGase), which were closely associated with the levels of free and conjugated PAs, were also detected. Results showed that under osmotic stress, the increases of the levels of non-covalently conjugated (non-CC) spermidine (Spd) and spermine (Spm), covalently conjugated (CC) putrescine (Put) and Spd in the plasma membrane of drought-tolerant Ganli No. 5 were more significant than those of drought-sensitive Suli No. 3, indicating that these conjugated PAs might be involved in the tolerance of plum seedlings to stress. Furthermore, the conjugated PAs were closely correlated with plum seedling growth, water retention capacity, plasma membrane damage degree, and hydrogen (H+)-ATPase activity in the plasma membrane. To get more complementary pieces of evidence, we subjected plum seedlings to combined treatments of PEG and exogenous PA (Spd and Spm), and an inhibitor of SAMDC [methylglyoxal-bis (guanylhydrazone), (MGBG)] or TGase (o-phenanthroline). These results collectively suggested that non-CC Spd and Spm, CC Put and Spd in plasma membrane might function in enhancing the tolerance of plum seedlings to osmotic stress by stabilizing membrane structure and therefore elevating H+-ATPase activity.

Phytochemicals Accumulation in Sanhua Plum ( Prunus salicina L.) during Fruit Development and Their Potential Use as Antioxidants.

This study followed the flesh reddening of Sanhua plum from the surface to the center during fruit development. Five key stages were identified based on color changes during fruit ripening: full-green (FG), red-appeared, half-red, full-red, and purple-red (PR). Fruits were collected and analyzed for phytochemicals and antioxidant properties. Concurrently, the transcript levels of genes associated with phenolic, flavonoid, and anthocyanin production were investigated. The titratable acid content of Sanhua plum decreased during development, while total soluble sugar content increased. In addition, both the total phenolic content and total flavonoid content decreased during development, while anthocyanin content increased. The polyphenol oxidase activity peaked in the PR stage. The maximum antioxidant activity in vitro was observed in the FG stage, while cellular antioxidant activity peaked in the PR stage.

Influence of rutin and ascorbic acid in colour, plum anthocyanins and antioxidant capacity stability in model juices.

Model juices at pH 3.7 were prepared with different combinations of ascorbic acid, rutin (quercetin 3-rutinoside) and concentrated anthocyanin extract of plums (cv. Black Gold). The anthocyanins in the concentrated extract were cyanidin 3-glucoside and cyanidin 3-rutinoside, in a proportion of 76% and 24% respectively. The model juices were stored during 17 weeks in darkness at 20 °C. The colour stability was improved by the presence of rutin and strongly damaged by the ascorbic acid. The fortification of anthocyanin model juices with ascorbic acid originated the degradation of most of anthocyanins. However, anthocyanins improved ascorbic acid stability during storage. The copigmentation of anthocyanin and rutin showed a beneficial effect on colour stability from the 5 weeks of storage. In model juices prepared exclusively with purified plum extract a high correlation (R(2)=0.881) between anthocyanins and antioxidant capacity was found.