Mechanism Investigation Of Chilling-induced Lignification Based On Ethylene Signal Transduction Elements In Postharvest Loquat Fruit

Loquat (Eriobotrya japonica Lindl.) is a non-climacteric fruit, with some cultivars such as 'Luoyangqing'(LYQ) and 'Dahongpao'(DHP) susceptible to chilling injury (CI), while others such as'Baisha'(BS) are resistant. Different levels of ethylene signal transduction elements were isolated and their expression patterns were investigated in loquat fruit at different developmental stages and under different postharvest conditions. These genes were differentially responsive to ethylene,1-methycyclopropene (1-MCP), low temperature conditioning (LTC) and heat shock (HS) treatments. Main results are as follows:1. By using degenerate primers and suppression subtractive hybridization (SSH) cDNA library, three ethylene receptor genes, one EjCTRl gene, one EjEIL1 gene, and four EjERFs were isolated and characterized in ripening loquat fruit. All of these genes were expressed in all tissues tested, including young root, young stem, young leaf, petal in full flowering stage, and fruit at different developmental stages. EjERS1a, EjCTR1, EjERF2 and EjERF3 maintained higher expression levels from 8 to 12 WAA, suggesting an important role that ethylene signalling played during the rapid fruit growth stages.2. During loquat fruit ripening, all nine genes showed constant or decreased expression patterns in reponse to low level of endogenous ethylene, especially in LYQ cultivar. However, transcripts of EjERS1a, EjERS1b, EjCTR1, EjERF2 and EjERF3 were significantly induced by exogenous ethylene, indicating that external ethylene can stimulate non-climacteric fruit ripening through ethylene signalling.3. During low temperature storage, EjETR1, EjCTR1, EjEIL1, EjERF1 and EjERF2 genes showed increased expression pattern and this was particularly notable for EjETR1, EjEIL1 and EjERF1 during CI development in LYQ fruit. Though both LTC and 1-MCP treatments can alleviate chilling-induced lignification, regulation of CI development by ethylene signalling may differ in these two treatments:LTC may alleviate CI through the regulation of EjEILl while 1-MCP may alleviate CI through the regulation of EjETRl at the transcriptional level. These results further indicate that EjEIL1 may directly respond to low temperature, while EjETR1 may directly responed to ethylene. Furthermore, the effect of CI alleviation was more pronounced with LTC treatment than that with 1-MCP treatment, suggesting EjEIL1 might be a more important regulation site for CI prevention in LYQ fruit.4. In response to high temperature, ethylene production increased and showed a peak in both LYQ and DHP loquat fruit. Expression patterns of EjERS1a, EjERS1b and EjERF2 during or after high temperature treatment were paralleled with the changes in such ethylene production, suggesting an important role of these genes played in high temperature stress response. Higher expression levels of EjHSP70 and EjERF2 genes were observed in HS treatment, especially in DHP cultivar, which showed better alleviation effect of CI symptom by HS.In conclusion, ethylene signalling regulates not only the development and postharevest ripening of non-climacteric loquat fruit, and it regulates chilling-induced lignification by different elements as well. Our study may fullfil the biological theory of ethylene transduction in the regulation of ripening and CI of non-climacteric fruit.