MicroRNAs (miRNAs) are small non-coding RNA molecules that function as diverse endogenous gene regulators at the post-transcriptional level. In the past two decades, as research effort on miRNA identification, function and evolution has soared, so has the demand for miRNA databases. However, the current plant miRNA databases suffer from several typical drawbacks, including a lack of entries for many important species, uneven annotation standards across different species, abundant questionable entries, and limited annotation. To address these issues, we developed a knowledge-based database called Plant miRNA Encyclopedia (PmiREN, http://www.pmiren.com/), which was based on uniform processing of sequenced small RNA libraries using miRDeep-P2, followed by manual curation using newly updated plant miRNA identification criteria, and comprehensive annotation. PmiREN currently contains 16,422 high confidence novel miRNA loci in 88 plant species and 3,966 retrieved from miRBase. For every miRNA entry, information on precursor sequence, precursor secondary structure, expression pattern, clusters and synteny in the genome, potential targets supported by Parallel Analysis of RNA Ends (PARE) sequencing, and references is attached whenever possible. PmiREN is hierarchically accessible and has eight built-in search engines. We believe PmiREN is useful for plant miRNA cataloguing and data mining, therefore a resource for data-driven miRNA research in plants.

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Xylitol, a five-carbon sugar alcohol, is a valuable sugar substitute, and widely used in the pharmaceutical, odontological and food industry due to its interesting properties. In the past decades, the xylitol industry has grown rapidly and more attention has been focused on xylitol purification, which possesses an important proportion of the whole industry. In our paper, the purification and crystallization of xylitol fermentation broth by biotechnology using corncob hydrolysates as substance were studied. An initial xylitol fermentation broth was decolored with activated carbon (1% M-1, 60°C, 165 rpm), desalted with a combination of two ionexchange resins (732 and D301), and residual sugars were separated with UBK-555(Ca 2+ ). Then the solution was vacuum-concentrated up to supersaturation (750 g/L xylitol). After adding 1% xylitol crystal seeds, the supersaturated solution was cooled to -20°C for 48 h. The crystalline xylitol of a regular tetrahedral shape with purity 95% and crystallization yield 60.2% was obtained from the clarified xylitol fermentation broth. An intact, economical and environmental-friendly route of purification and crystallization of xylitol from fermentation of corncob hydrolysates was obtained, and its experimental procedure and data provided a sound basis for large-scale industrial production.

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