Melatonin plays important roles in various aspects of biological processes. However, it is less known on the effects and mechanism of melatonin on the postharvest physiological deterioration (PPD) process of cassava, which largely restricts the potential of cassava as a food and industrial crop. In this study, we found that exogenous application of melatonin significantly delayed PPD of cassava tuberous roots by reducing H2O2 content and improving activities of catalase and peroxidase. Moreover, 3425 differentially expressed genes by melatonin during the PPD process were identified by transcriptomic analysis. Several pathways were markedly affected by melatonin treatments, including metabolic-, ion homeostasis-, and enzyme activity-related processes. Further detailed analysis revealed that melatonin acted through activation of ROS-scavenging and ROS signal transduction pathways, including antioxidant enzymes, calcium signaling, MAPK cascades, and transcription factors at early stages. Notably, the starch degradation pathway was also activated at early stages, whereas it was repressed by melatonin at middle and late stages, thereby indicating its regulatory role in starch metabolism during PPD. Taken together, this study yields new insights into the effect and underlying mechanism of melatonin on the delay of PPD and provides a good strategy for extending shelf life and improvement of cassava tuberous roots.

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Cassava (Manihot esculenta) shows strong tolerance to drought stress; however, the mechanisms underlying this tolerance are poorly understood. Ethylene response factor (ERF) family genes play a crucial role in plants responding to abiotic stress. Currently, less information is known regarding the ERF family in cassava. Herein, 147 ERF genes were characterized from cassava based on the complete genome data, which was further supported by phylogenetic relationship, gene structure, and conserved motif analyses. Transcriptome analysis suggested that most of the MeERF genes have similar expression profiles between W14 and Arg7 during organ development. Comparative expression profiles revealed that the function of MeERFs in drought tolerance may be differentiated in roots and leaves of different genotypes. W14 maintained strong tolerance by activating more MeERF genes in roots compared to Arg7 and SC124, whereas Arg7 and SC124 maintained drought tolerance by inducing more MeERF genes in leaves relative to W14. Expression analyses of the selected MeERF genes showed that most of them are significantly upregulated by osmotic and salt stresses, whereas slightly induced by cold stress. Taken together, this study identified candidate MeERF genes for genetic improvement of abiotic stress tolerance and provided new insights into ERF-mediated cassava tolerance to drought stress.

DNA-barcoding approaches to estimate the diet compositions of grazing animals have received significant attention, and particularly when combined with next-generation sequencing, these techniques have substantially improved in recent years. In this study, the identity and species composition of plant material ingested by Mongolian sheep were estimated through the use of 350 bp ITS2 gene sequences of the vegetation found in fecal samples. Four diets were formulated using varying amounts of eight plant species that are common in the grasslands of northern China. Sixteen Mongolian sheep were taken from pastures and randomly assigned to four groups, and each group received one of four diets. Each sheep was randomly assigned to one of 16 confinement pens and fed its respective diet for 12 consecutive days. Fecal samples were removed from each pen from days 7-12, preserved, and composited for each pen. All herbage species included in the daily diets were detected in each fecal sample, with the exception of Phragmites australis. Moreover, 12 additional different plant species were retrieved from feces of the experimental sheep. The obtained data provided preliminary support for the use of the ITS2 barcode to determine which plants were consumed. Moreover, the proportions of the herbage DNA sequences recovered from sheep feces and those of the herbage masses in the daily diets did not completely match. These results indicate that the non-Gramineae DNA sequences amplified with ITS2 primers (including those of Chenopodium album, Artemisia scoparia, Artemisia tanacetifolia, and Medicago sativa) far exceeded those of the Gramineae species (including Leymus chinensis and Puccinellia distans), which constitute the largest share of the experimental diets. A significant positive correlation (Spearman's ρ = 0.376, P = 0.003) between the actual herbage mass proportions in the experimental diets and the herbage-DNA-sequence proportions provided sufficiently favorable support for the further investigation of DNA barcoding for the quantification of plants in feces. A significant regression coefficient was found between the relative DNA-sequence proportions of L. chinensis ( R = 0.82, P < 0.0001), P. distans ( R = 0.64, P = 0.0017), and C. album ( R = 0.98, P < 0.0001) and their respective herbage mass proportions. The quantitative relationship can be expressed by the linear-regression equations y = 0.90 x - 0.22, y = 0.98 x - 0.03, and y = 5.00 x - 0.25, respectively. Thus, these results demonstrate that dietary-DNA-barcoding methods exhibited potential in providing valuable quantitative information regarding food-item components. However, it should be noted that this explorative data needs to be further improved by using additional genes and by creating a sophisticated reference database, thus enhancing both quality and accuracy of the obtained results.

Effects of different potassium (K) levels, which were K0 (no fertilizer), K1 (71.5 g KCl plant−1 year−1), K2 (286.7 g KCl plant−1 year−1), and K3 (434 g KCl plant−1 year−1), were evaluated based on sugar and organic acid metabolism levels from 70–126 days after bloom (DAB) in the developing fruit of potted five-year-old apple (Malus domestica, Borkh.) trees. The results indicate that K fertilization promoted greater fruit mass, higher Ca2+ and soluble solid levels, and lower titratable acid levels, as well as increased pH values at harvest. With the application of different levels of K fertilizer, fructose, sorbitol, glucose and sucrose accumulation rates significantly changed during fruit development. Fruit in the K2 group had higher fructose, sucrose and glucose levels than those in other treatment groups at 126 DAB. These changes in soluble sugar are related to the activity of metabolic enzymes. Sucrose synthase (SS) and sorbitol dehydrogenase (SDH) activity in the K2 treated fruit was significantly higher than those in other treatment groups from 70–126 DAB. Malate levels in K-supplemented fruit were notably lower than those in non K-supplemented fruit, and K3 treated fruit had the lowest malate levels during fruit development. Cytosolic malic enzyme (ME) and phosphoenolpyruvate carboxykinase (PEPCK) activity significantly increased in fruit under the K2 treatment during 112–126 DAB and 98–126 DAB, respectively. In addition, Ca2+ concentration increased with increasing K fertilization levels, which promoted a maximum of 11.72 mg g−1 dry weight in apple fruit. These results show that K levels can alter soluble sugar and malate levels due to the interaction between sugars and acid-metabolic enzymes in fruit.

A real-time quantitative PCR assay using a species-specific primer pair was developed to rapidly and accurately quantify Valsa mali , the causative pathogen of apple Valsa canker (AVC), in crabapple seeds, crabapple seedlings, apple twigs and apple seeds. Surveys were conducted in different regions, and crabapple or apple seeds were collected for V . mali detection by qPCR assay. Our results showed that 12.87% to 49.01% of crabapple seeds collected from different regions were positive for V . mali . The exopleura and endopleura were the two major areas of V . mali infection in crabapple seeds. The presence of V . mali infection in crabapple seeds was also confirmed by a high-throughput sequencing approach. With the growth of crabapple seedlings, the concentration of V . mali gDNA in crabapple seedlings gradually increased until eight or more leaf blades emerged. One-year-old twigs from an apple scion nursery were infected with V . mali , and only apple seeds from infected apple trees showing evident Valsa canker symptoms carried V . mali . In conclusion, this study reports that crabapple seeds and apple seeds carried V . mali as latent inoculum sources. V . mali infected not only apple tissues but also crabapple seedlings, which are the rootstocks of apple trees. This study indicated that the inoculum sources for AVC vary. Application of a novel qPCR assay can potentially improve the accuracy of early diagnosis, and is helpful to reveal the epidemic regularity of AVC.