MicroRNAs and targets in senescent fruit of litchi during ambient storage and post cold storage shelf-life.

Background: Litchi has high commercial value for its bright color and rich nutrients. However, it deteriorates with the pericarp turning brown within 1-2 days after harvest. The factors that mediate litchi fruit senescence are complicated. MicroRNAs act as negative regulators involving in almost every physiological process. To understand the mechanism of litchi fruit senescence and pericarp browning from miRNA level, five small RNA libraries and a degradome library from the pericarp of litchi fruit stored at ambient and post cold shelf-life were sequenced. Results: By aligning the sRNA reads onto litchi unigene assembly, 296 miRNAs belonging to 49 known miRNA families were first identified from litchi. In addition, eleven litchi-specific miRNAs were identified. Among these, 167 known miRNAs were identified to cleave 197 targets, and three litchi-specific miRNAs were found to have five targets. Through combined analysis of stem-loop quantitative real-time polymerase chain reaction (qRT-PCR) and transcriptome profiling, 14 miRNA-target pairs were found to be actively involved in litchi fruit senescence-related processes, including energy regulation, anthocyanin metabolism, hormone signaling, and pathogen-infection defense. Conclusions: A network of miRNA-target that regulates litchi fruit senescence has been proposed, revealing the miRNA-mediated regulation in senescent litchi fruit. This will aid to develop new strategies to postpone the senescence of litchi fruit and other horticultural products. Overall design: Examination of miRNAs in litchi pericarp tissue at 5 specific stages relating to ambient and post cold storage. Table S1.xlsx: statistics of sRNA sequences from litchi pericarp Table S2.xlsx: conserved miRNAs identified from litchi pericarp Table S3.xlsx: predicted candidate litchi-specific miRNAs Table S4.xlsx: detailed table of degradome sequencing data