Author(s): Xiangbin Xu 1, Lili Yin 1, Qicai Ying 1, Hongmiao Song 1,*, Dawei Xue 1, Tongfei Lai 1, Maojun Xu 1, Bo Shen 1,*, Huizhong Wang 1,*, Xuequn Shi 2,*
Fruits are essential component of the human diets, especially from fleshy species, which contain high levels of vitamins, antioxidants and dietary fiber. According to the ripening characteristic, fleshy fruits are designated as climacteric and non-climacteric . Climacteric fruits are characterized by a burst of respiration at the onset of ripening along with a large rise in ethylene production, such as the apple, banana, peach and tomato. They can ripen off the parent plant and get soft and sweet after harvest, and can be picked before the fully ripe stage to maintain quality and extend storage life. Besides, their ripening can be initiated by exposure to exogenous ethylene. In non-climacteric fruits, the respiratory increase is absent and no phytohormone is appearing to be critical for the ripening process, and they can not be initiated by exogenous phytohormone. They must remain on the parent plant to enable full ripening and be picked at or near the fully ripe stage to obtain the best eating quality. However, at ambient temperature, some of the non-climacteric fruits post-harvest senescence occurs very quickly, such as strawberry and cherry, and their storage time is only 2-3 d, which often serious affects fruit quality and marketing value, and causes huge losses. Thus, studies of the complex molecular mechanism of non-climacteric fruits post-harvest senescence and technologies for extending their storage life have attracted considerable attentions.
In recent years, small RNAs (sRNAs) are getting more and more attention for their key roles in post-transcriptional or translational gene regulation -. Small interfering RNAs (siRNAs) and microRNAs (miRNAs) are the two major groups of sRNAs. The miRNAs are short (20 to 24 nucleotides in length), single strand and endogenous non-coding sRNAs molecules that negatively regulate gene expressions at post-transcriptional level identified in nearly all eukaryotes , . The miRNA genes originate in the nucleus, where they are encoded by independent transcriptional units in intergenic regions and transcribed by RNA polymerase II to form pri-miRNA. In plant, the stem loop region of pri-miRNAs are cut by Dicer endonuclease to form small double stranded RNA (dsRNA) miRNA: miRNA* and then transported to cytoplasm by HST , . Then the miRNA* strand is degraded by SDN and the miRNA strand is incorporated in the RNA-induced silencing complex (RISC) with endonuclease AGO , where they serving as a leading RNA to direct cleavage of complementary mRNAs . Recent studies have revealed the key roles of miRNAs in diverse biological processes such as development, hormone response and stresses response -. Several miRNAs also have been found to be effective in regulating different mechanisms entailing plant senescence. For example, miR319 negatively regulates leaf growth and positively regulates leaf senescence by modulating the activity of TCP transcription factors . MiR164 prevents premature overexpression of ORE1 , a positive regulator of ageing-induced cell death and senescence, and regulates the...