Analysis Of Differential Proteomes And Expression Profiling Of Lignification-related Transcription Factors During Peach Hardening

Peach(Prunus persica) is one of the economically important fruit crops in China, and also one of the model species in Rosaceae. Peach fruit is similar to other drupes, and featured with a hard lignified endocarp, which surrounding the seed.In order to investigate the development and formation of endocarp, peach cutivar 'Ohkubo'was used as material and several approaches were employed. The growth parameters and lignin deposition process were observed to determine hardening period; a proteomic approach based on two-dimensional electrophoresis together with mass spectrometry was used to explore the differentially expressed proteins; two NAC and four MYB transcription factor genes were cloned, and their expression patterns were examined. The main results and conclusions are as follows.(1) Analysis of growth parameters and lignin deposition revealed that the lignification of endocarp occurred in the transition period from the young fruit fast-growing stage to the fruit hardening period stage (between35and45days after flowering). During this period, the lignin deposition process featured a rapid expansion from seed cavity to the peripheral region of the endocarp, and the change of lignin content also fitted to an exponential growth curve.(2) Sixty-eight protein spots with different expression patterns were identified in both the endocarp and mesocarp during pit hardening, and the majorities were involved in primary or secondary metabolism. In contrast to most proteins associated with primary metabolism in the endocarp, whose expression is down-regulated, expression of pyruvate dehydrogenase (PDH) unexpectedly increased exponentially (up to19.9-fold). Moreover, its expression pattern was linearly positively correlated with the exponentially growing lignin content (R=0.940), which suggests that PDH may play a role in endocarp lignification. The proteome data also revealed different spatiotemporal expressions of enzymes involved in the lignin and flavonoid pathways that provided proteome-level evidence to support the hypothesis that these two pathways are competitive during endocarp development. In addition, the endocarp-specific oxidative stress was also observed and proposes that it may act as a stimulating factor in activating lignification and subsequent programmed cell death in the endocarp.(3) Two NAC domain and four MYB domain transcription factor genes were isolated from peach endocarp by homologous cloning method. The amino acid sequence alignment and phylogenetic analysis results indicated they were closely related to secondary cell wall formation-and lignification-related transcription factors in Populus trichocarpa and Arabidopsis thaliana. Quantitative real-time PCR analysis showed that the expression patterns of them were dramatically up-regulated during the lignification of peach endocarp (up to15.0to325.2-fold)), and their transcript expression levels were more abundant in endocarp than in mesocarp. Moreover, the expression analysis of the putative downstream targets of them suggested that they may play important role in endocarp developmental lignification.