Dendrobium moniliforme (D. moniliforme) is a traditional medicinal herb widely cultivated in Asia. Flavonoids, one of the largest groups of secondary metabolites in plants, are significant medicinal components in Dendrobium species. Several subgroups of R2R3-MYB proteins have been validated to directly regulate flavonoid biosynthesis. Using PacBio sequencing technology, we assembled a high-quality chromosome-level D. moniliforme genome with a total length of 1.20 Gb and a contig N50 of 3.97 Mb. The BUSCO assessment of genome annotation was 91.4%. By integrating the genome and transcriptome, we identified biosynthesis pathway enzyme genes related to flavonoids, polysaccharides, carotenoids, and alkaloids. A total of 90 R2R3-MYBs were identified in D. moniliforme and classified into 21 subgroups. Studies on the functions of R2R3-MYB transcription factors revealed that R2R3-MYB in SG6 can up-regulate flavonoid biosynthesis. Various validation experiments, including subcellular localization, transient overexpression, UPLC-MS/MS, HPLC, yeast one-hybrid, and dual-luciferase assays, demonstrated that DMYB69 directly up-regulates the expression of enzyme genes involved in flavonoid biosynthesis, increasing the content of flavonoids such as anthocyanin, flavone, and flavonol. Additionally, DMYB44 was shown to directly up-regulate the expression of carotenoid biosynthesis enzyme genes, thereby increasing carotenoid content. This study provides an essential genome resource and theoretical basis for molecular breeding research in D. moniliforme.

Objective:To investigate the effects of marathon exercise on knee cartilage volume and T2 relaxation time (T2 value) based on MRI.Methods:From December 2018 to December 2021, 25 healthy volunteers without long-distance running habits and 32 non-professional marathon runners with long-term long-distance running were recruited to undergo knee MRI 3D water-selective excitation (three dimensional water-selective excitation, 3D-WATS) and T2 mapping imaging were performed, and the cartilage volumes in 5 knee areas and T2 values in 42 subareas were extracted for analysis. To compare the cartilage volume and its ratio to body surface area of knee joint of healthy volunteers and non-professional marathon runners, the T2 value of cartilage in each subregion, and the correlation between marathon exercise intensity and the volume and T2 value of cartilage in different regions.Results:Compared with healthy volunteers, there was no significant difference in cartilage volume or the ratio of body surface area to body volume of non-professional marathon runners ( P>0.05). There were significant differences between healthy volunteers and non-professional marathon runners in cartilage T2 values of the median layer of medial condyle of femur (47.61±5.65 ms and 44.29±6.10 ms) and the deep layer of medial condyle of femur (36.82±9.05 ms and 31.67±7.59 ms), deep precondylar area of medial femur (38.37±4.68 ms and 34.09±4.19 ms), shallow area of medial condylar area of femur (52.17±11.11 ms and 45.51±7.76 ms), middle layer of medial condylar area of femur (49.09±5.08 ms and 45.63±5.04 ms), medial layer of anterior condylar region of lateral femur (45.69±4.68 ms and 42.57±5.77 ms), superficial layer of posterior condylar region of lateral femur (55.42±18.41 ms and 47.99±8.39 ms), deep layer of anterior tibial medial plateau (33.40±7.76 ms and 29.03±5.69 ms), deep layer of posterior tibial medial plateau (31.28±5.02 ms and 27.92±5.99 ms), deep layer of patellofemoral surface (35.65±6.99 ms and 32.30±5.28 ms), respectively ( P<0.05). In non-professional marathon runners, the medial tibial plateau cartilage volume was negatively correlated with step frequency ( r=-0.371, P=0.035), the lateral femoral condylar cartilage volume was negatively correlated with step frequency ( r=-0.365, P=0.043), and the lateral tibial plateau cartilage volume was negatively correlated with step frequency ( r=-0.550, P=0.001). The T2 value of the medial layer cartilage in the anterior tibial medial plateau region was negatively correlated with body weight ( r=-0.277, P=0.039) and body mass index ( r=-0.290, P=0.030). The T2 value of the superficial layer of patellofemoral surface was negatively correlated with the amount of running in 3 months ( r=-0.457, P=0.010). The superficial T2 value in the posterior lateral plateau of the tibia was negatively correlated with stride length ( r=-0.437, P=0.014), and the medial layer cartilage T2 value in the anterior condylar area of the lateral femur was negatively correlated with stride frequency ( r=-0.380, P=0.035). Conclusion:Marathon exercise had little effect on the knee cartilage volume, but had a certain effect on the cartilage T2 value, resulting in changes in cartilage structure. The higher the step frequency, the smaller the cartilage volume. The greater the body weight or body mass index, the greater the amount of running in 3 months, and the greater the stride length, the lower the cartilage T2 value.