Transcriptome analysis of Chinese bayberry (Myrica rubra Sieb. et Zucc.) fruit treated with heat and 1-MCP.

Chinese bayberry (Myrica rubra Sieb. et Zucc.) is a typical fruit tree grown in the hilly region of Southern China. The fruit is sensitive to storage and transportation conditions and presents a major problem in its commercialization. The present study was conducted to investigate the regulation of gene expression involved in plant hormone signaling pathway in the Chinese bayberry with different treatments of heat and 1-methylcyclopene (1-MCP) during postharvest storage. In one treatment group (HM group), we exposed Chinese bayberry fruit to 48 °C for 10 min and then sealed them in a desiccator with 5 µl·L-1 of 1-MCP for 24 h at 20 °C, followed by storage at 10 °C. Another group (CK group) was directly stored at 10 °C without any prior treatment. Samples of fruit were collected every three days, at 3, 6, 9, 12 and 15 d (CK3, CK6, CK9, CK12 and CK15; and HM3, HM6, HM9, HM12, and HM15, respectively). The decay index of fruits in the CK group increased after six days of storage but did not increase until nine days of storage in the HM group. Superoxide dismutase (SOD) activity in the CK group was shown a downtrend during storage, and almost no fluctuation from six days. In the HM group, SOD activity increased after three days, but decreased sharply after six days storage. Besides, peroxidase (POD) and catalase (CAT) activities were shown the similar trend during the storage, both of them first increased and then decreased form the six days of storage. These physiological data indicated that the sixth day is a crucial time during the storage of Chinese bayberry treated with heat and 1-MCP. Therefore, the transcriptome libraries were constructed from CK0, CK6, HM6 group, respectively. The analysis of top 20 KEGG pathways showed that most differentially expressed genes were involved in the biosynthesis of secondary metabolites, particularly flavonoids and flavanols biosynthesis, in CK0 vs. CK6 and CK0 vs. HM6. However, the top three KEGG pathways in CK6 vs. HM6 were the ribosome, RNA transport and endocytosis during the storage. Expression of six ethylene receptor (ETR) genes and four ethylene-responsive transcription factor (ERF) genes were activated at transcriptional level during the postharvest stage and were decreased by heat and 1-MCP treatment, and serine/threonine-protein kinase 1 (CTR1) was also repressed by treatment. Abscisic acid (ABA) -responsive element binding factor (ABF) gene, auxin-responsive GH3 gene and transcription factor MYC2 gene also showed similar expression pattern with ethylene pathway genes. These results might improve our understanding of the mechanisms of heat and 1-MCP inhibition of fruit postharvest physiology and prolongation of fruit shelf life.

How did nature engineer the highest surface lipid accumulation among plants? Exceptional expression of acyl-lipid-associated genes for the assembly of extracellular triacylglycerol by Bayberry (Myrica pensylvanica) fruits.

Bayberry (Myrica pensylvanica) fruits are covered with a remarkably thick layer of crystalline wax consisting of triacylglycerol (TAG) and diacylglycerol (DAG) esterified exclusively with saturated fatty acids. As the only plant known to accumulate soluble glycerolipids as a major component of surface waxes, Bayberry represents a novel system to investigate neutral lipid biosynthesis and lipid secretion by vegetative plant cells. The assembly of Bayberry wax is distinct from conventional TAG and other surface waxes, and instead proceeds through a pathway related to cutin synthesis (Simpson and Ohlrogge, 2016). In this study, microscopic examination revealed that the fruit tissue that produces and secretes wax (Bayberry knobs) is fully developed before wax accumulates and that wax is secreted to the surface without cell disruption. Comparison of transcript expression to genetically related tissues (Bayberry leaves, M. rubra fruits), cutin-rich tomato and cherry fruit epidermis, and to oil-rich mesocarp and seeds, revealed exceptionally high expression of 13 transcripts for acyl-lipid metabolism together with down-regulation of fatty acid oxidases and desaturases. The predicted protein sequences of the most highly expressed lipid-related enzyme-encoding transcripts in Bayberry knobs are 100% identical to the sequences from Bayberry leaves, which do not produce surface DAG or TAG. Together, these results indicate that TAG biosynthesis and secretion in Bayberry is achieved by both up and down-regulation of a small subset of genes related to the biosynthesis of cutin and saturated fatty acids, and also implies that modifications in gene expression, rather than evolution of new gene functions, was the major mechanism by which Bayberry evolved its specialized lipid metabolism. This article is part of a Special Issue entitled: Plant Lipid Biology edited by Kent D. Chapman and Ivo Feussner.

Amplicon restriction patterns associated with nitrogenase activity of root nodules for selection of superior Myrica seedlings.

Trees of Myrica sp. grow abundantly in the forests of Meghalaya, India. These trees are actinorhizal and harbour nitrogen-fixing Frankia in their root nodules and contribute positively towards the enhancement of nitrogen status of forest areas. They can be used in rejuvenation of mine spoils and nitrogen-depleted fallow lands generated due to slash and burn agriculture practiced in the area. We have studied the association of amplicon restriction patterns (ARPs) of Myrica ribosomal RNA gene and internal transcribed spacer (ITS) region and nitrogenase activity of its root nodules. We found that ARPs thus obtained could be used as markers for early screening of seedlings that could support strains of Frankia that fix atmospheric nitrogen more efficiently.

Diarylheptanoid sulfates and related compounds from Myrica rubra bark.

Three new diarylheptanoids, myricanol 11-sulfate (1), juglanin B 11-sulfate (2), and myricanone 5-O-(6'-O-galloyl)glucoside (3), were isolated from the bark of Myrica rubra. Compounds 1 and 2 were characterized as diarylheptanoid sulfates on the basis of spectroscopic analyses. The antioxidative activities of the fractionated extracts and isolated compounds were estimated by the oxygen radical absorbance capacity (ORAC) and superoxide dismutase (SOD)-like activity assays. The major isolate, myricitrin (4), displayed a high ORAC value and moderate SOD-like activity (13,198 µmol TE (Trolox equivalent)/g and IC50 127.5 µg/mL, respectively), which might explain the potent antioxidative activity of this material.

Transcriptomic analysis of Chinese bayberry (Myrica rubra) fruit development and ripening using RNA-Seq.

BACKGROUND: Chinese bayberry (Myrica rubra Sieb. and Zucc.) is an important subtropical fruit crop and an ideal species for fruit quality research due to the rapid and substantial changes that occur during development and ripening, including changes in fruit color and taste. However, research at the molecular level is limited by a lack of sequence data. The present study was designed to obtain transcript sequence data and examine gene expression in bayberry developing fruit based on RNA-Seq and bioinformatic analysis, to provide a foundation for understanding the molecular mechanisms controlling fruit quality changes during ripening. RESULTS: RNA-Seq generated 1.92 G raw data, which was then de novo assembled into 41,239 UniGenes with a mean length of 531 bp. Approximately 80% of the UniGenes (32,805) were annotated against public protein databases, and coding sequences (CDS) of 31,665 UniGenes were determined. Over 3,600 UniGenes were differentially expressed during fruit ripening, with 826 up-regulated and 1,407 down-regulated. GO comparisons between the UniGenes of these two types and interactive pathways (Ipath) analysis found that energy-related metabolism was enhanced, and catalytic activity was increased. All genes involved in anthocyanin biosynthesis were up-regulated during the fruit ripening processes, concurrent with color change. Important changes in carbohydrate and acid metabolism in the ripening fruit are likely associated with expression of sucrose phosphate synthase (SPS) and glutamate decarboxylase (GAD). CONCLUSIONS: Mass sequence data of Chinese bayberry was obtained and the expression profiles were examined during fruit ripening. The UniGenes were annotated, providing a platform for functional genomic research with this species. Using pathway mapping and expression profiles, the molecular mechanisms for changes in fruit color and taste during ripening were examined. This provides a reference for the study of complicated metabolism in non-model perennial species.

Effect of hot air treatment on postharvest mould decay in Chinese bayberry fruit and the possible mechanisms.

The effect of hot air treatment (HAT) on reducing natural fungal decay and green mould decay caused by Leptographium abietinum on postharvest Chinese bayberry fruit and the possible mechanisms were investigated. Freshly harvested Chinese bayberry fruit were firstly pretreated with hot air at 36-60 degrees C for 1-3h, and then stored at 20 degrees C for 3d or at 1 degrees C for 12d to investigate the optimum condition of hot air treatment (HAT) for inhibiting decay development. Results demonstrated that HAT at 48 degrees C for 3h was the most effective in reducing natural decay without impairing quality. This treatment also enhanced the resistance of Chinese bayberry fruit against green mould rot caused by L. abietinum and reduced the severity of the disease. The activities of defense-related enzymes including chitinase, beta-1, 3-glucanase, peroxidase and polyphenol oxidase were significantly enhanced by HAT. In addition, the in vitro experiment showed that HAT significantly inhibited spore germination, germ tube elongation and mycelial growth of L. abietinum. These results indicate that HAT can effectively reduce fruit decay possibly by directly inhibiting pathogen growth and indirectly inducing disease resistance.

[Inhibition of postharvest decay and induction of defensive enzymes by pure oxygen in Chinese bayberry fruit].

Chinese bayberry fruits were stored in air (control) or pure oxygen atmosphere for up to 12 days at 5 degrees C to investigate the effects of high oxygen on decay control and its relation to the induction of defensive enzyme activities. The results showed that exposure of Chinese bayberry to pure oxygen significantly prevented fruit decay. At the end of the storage period, the decay index of fruits exposed to pure oxygen was only 17% while that of control fruits reached 54% (Fig.1). Pure oxygen caused a significant increase in chitinase and beta-1,3-glucanase activities which reached a peak on the 6th day of storage (Fig.2). Phenylalanine ammonium-lyase (Fig.3A) and peroxidase (Fig.4) activities as well as total phenolic content (Fig.3B) increased more quickly and stayed at significantly higher levels in fruits exposed to pure oxygen during storage than the control fruits. These results suggest that the inhibition of postharvest fruit decay by high oxygen was related to the induction of defensive enzyme activities. The induced disease resistance may be involved in the mechanisms by which high oxygen treatment inhibited fruit decay in Chinese bayberry.