The Characterization Of PRX Involved In Chilling Induced Lignification Of Postharvest Loquat Fruit And Its Transcriptional Regulation

Loquat(Eriobotrya japonica Lindl.)originates from subtropical area of China.Due to the high temperature and humidity during harvest season,the low temperature storage and cold chain(0?)logistics are often applied to prolong its storage time.However,red fleshed cultivars,such as 'Luoyangqing'(LYQ),are prone to exhibit lignification during low temperature storage(0?),with the increase of fruit firmness and accumulation of lignin content,which would subsequently influence fruit flavor and commercial value.In the present study,'LYQ'fruit was used as material,treated with heat treatment(HT)and low temperature conditioning(LTC)to delay the chilling(0?)induced lignification.Then,with the help of transcriptomics analysis,as well as qRT-PCR,yeast one hybrid,dual luciferase assay and EMSA,the lignification related EjPRX gene and its transcriptional regulator(bZIP)were identified.The main results are as follows:1.EjPRX5 was characterized as one of the main contributors for lignin accumulation in loquat fruit.Based on RNA-seq,eight PRXs were isolated and characterized,including five full length PRXs(EjPRX4-EjPRX8).Among them,EjPRX5 and EjPRX7 were positively correlated with flesh lignification,while EjPRX5 showed much higher abundance than EjPRX7(about 3335 times).In addition,the EjPRX5 transient overexpression led to accumulation of lignin content in the leaves of Nicotiana tabacum.Thus,EjPRX5 could be proposed as the key PRX for loquat fruit lignification.2.EjbZIP28,obtained by yeast one hybrid screening,participated in chilling induced lignification.Dual-luciferase assay manifested that EjbZIP28 could trans-activate the promoter of EjPRX5.Yeast one hybrid indicated that EjbZIP28 could physically interact with EjPRX5 promoter,which was further verified by EMSA and the specific binding site was G-box element(-128 to-98 bp region).Expression analysis indicated that EjbZIP28 was induced by 0? and inhibited by HT and LTC treatment,which coincides with the expression pattern of EjPRX5 and lignification process.Thus,it is speculated that EjbZIP28 plays an important role in the process of chilling induced lignification of postharvest loquat.In summary,this study identified the key PRX member(EjPRX5)for the chilling induced lignification of loquat fruit,and also pointed out that EjbZIP28 was a transcriptional activator for EjPRX5.All these findings indicated the novel mechanism of chilling induced lignification of loquat fruit.