Chokecherry (Padus virginiana L.) is an important landscaping tree with high ornamental value because of its colorful purplish-red leaves (PRL). The quantifications of anthocyanins and the mechanisms of leaf color change in this species remain unknown. The potential biosynthetic and regulatory mechanisms and the accumulation patterns of anthocyanins in P. virginiana that determine three leaf colors were investigated by combined analysis of the transcriptome and the metabolome. The difference of chlorophyll, carotenoid and anthocyanin content correlated with the formation of P. virginiana leaf color. Using enrichment and correlation network analysis, we found that anthocyanin accumulation differed in different colored leaves and that the accumulation of malvidin 3-O-glucoside (violet) and pelargonidin 3-O-glucoside (orange-red) significantly correlated with the leaf color change from green to purple-red. The flavonoid biosynthesis genes (PAL, CHS and CHI) and their transcriptional regulators (MYB, HD-Zip and bHLH) exhibited specific increased expression during the purple-red periods. Two genes encoding enzymes in the anthocyanin biosynthetic pathway, UDP glucose-flavonoid 3-O-glucosyl-transferase (UFGT) and anthocyanidin 3-O-glucosyltransferase (BZ1), seem to be critical for suppressing the formation of the aforesaid anthocyanins. In PRL, the expression of the genes encoding for UGFT and BZ1 enzymes was substantially higher than in leaves of other colors and may be related with the purple-red color change. These results may facilitate genetic modification or selection for further improvement in ornamental qualities of P. virginiana.

Cerasus humilis, grown in the northern areas of China, may experience water deficit during their life cycle, which induces oxidative stress. Our present study was conducted to evaluate the role of oxidative stress management in the leaves of twoC. humilisgenotypes, HR (drought resistant) and ND4 (drought susceptible), when subjected to a long-term soil drought (WS). The HR plants maintained lower membrane injury due to low ROS and MDA accumulation compared to ND4 plants during a long-term WS. This is likely attributed to global increase in the activities of superoxide dismutase (SOD) isoenzymes and enzymes of the ascorbate-glutathione (AsA-GSH) cycle and maintenance of ascorbate (AsA) levels. Consistent closely with enzymes activities, the expression of cytosolic ascorbate peroxidase (cAPX) and dehydroascorbate reductase (DHAR) followed a significant upregulation, indicating that they were regulated at the transcriptional level for HR plants exposed to WS. In contrast, ND4 plants exhibited high ROS levels and poor antioxidant enzyme response, leading to enhanced membrane damage during WS conditions. The present study shows that genotypic differences in drought tolerance could be likely attributed to the ability ofC. humilisplants to induce antioxidant defense under drought conditions.

Periodic drought fluctuation is a common phenomenon in Northwest China. We analyzed the response of Chinese dwarf cherry (Cerasus humilis) seedlings, a dwarf shrub species with considerably strong adaptabilities, exposed to water stress (WS) by withholding water for 21 d, and subsequent recovery of 7 d. Leaf relative water content (LRWC), net photosynthetic rate (P _N), maximal quantum yield of PSII photochemistry (F_v/F_m), and effective quantum yield of PSII photochemistry (Φ_PSII) decreased with increasing water deficit. In contrast, the nonphotochemical quenching of Chl fluorescence (NPQ) significantly increased, as well as the amounts of violaxanthin (V) + antheraxanthin (A) + zeaxanthin (Z). In the whole levels, the photosynthetic pigment composition did not display significant changes in WS seedlings. However, the de-epoxidation state of xanthophyll cycle pigments [(Z+0.5A)/VAZ ] generally exhibited higher values in WS seedlings. The significant inhibition of de-epoxidation by dithiothreitol (DTT) and negligible changes of epoxidation of Z by glucosamine (Gla) were both observed; the slight but stably upregulated transcript level of violaxanthin de-epoxidase (VDE) and downregulated zeaxanthin epoxidase (ZEP) expression profile were found during WS period, indicating that they were regulated on post-transcript levels. VDE activity, via the accumulation of Z and A, which confers a greater capacity of photoprotection, appears to contribute to the survival of severely stressed plants.

Cerasus humilis is a unique dwarf shrub and fruit color is an important trait in the species. In this study, we evaluated the transcriptomic and metabolomic profiles of the plant at different developmental stages to elucidate the mechanism underlying color formation. In a metabolomics analysis, 16 anthocyanin components were identified at four developmental stages, and high levels of cyanidin O-syringic acid and pelargonidin 3-O-beta-d-glucoside (callitephin chloride) were correlated with the reddening of the fruit peel. A co-expression analysis revealed that ANS and UFGT play key roles in pigmentation (PCC > 0.82). Additionally, transcriptome data showed that most anthocyanin biosynthetic genes and two MYB transcription factors were significantly up-regulated. QRT-PCR results for these differentially expressed genes were generally consistent with the high-throughput sequencing. Moreover, the overexpression of ChMYB1 (TRINITY_DN21536_c0_g1) in apple calli could contribute to the accumulation of anthocyanin. It was also found that UFGT (TRINITY_DN19893_c1_g5) and ChMYB1 (TRINITY_DN21536_c0_g1) have similar expression patterns. These findings provide insight into the mechanisms underlying anthocyanin accumulation and coloration during fruit peel development, providing a basis for the breeding of anthocyanin-rich C. humilis cultivars.