Proteomic Analysis Of Longan(Dimocarpus Longan Lour.) Seed Abortion

Proteomics study is playing an increasing important role in the functional genomics era. Two-dimensional electrophoresis is one of the key technique in proteomics studies. Aborted-seed longan is a rare brood in longan which is a famous evergreen fruit tree found in subtropical areas of the world.We optimized the longan seed protein extraction method and the electrophoresis conditions, and obtained the high-resolution and reproducible gel maps. At least 1000 protein spots were detected on the gels of longan seed. The correlation coefficient between replicates varied from 0.88-0.945.Furthermore, a proteomic method was used to study seed abortion in Dimocarpus longan Lour. (cv. Minjiao 64-1) by comparing normal and abortive seeds at three different development stages. 43 protein spots being differentially expressed at least at one stage. Of these differentially expressed proteins, 20 were up-regulated, 21 were down-regulated, and 2 showed more complex expression patterns. Thirty-five proteins were identified by matrix-assisted laser desorption ionization-time of flight-tandem mass spectrometry (MALDI-TOF-MS/MS) analysis and protein data searching. Identified rate was 82%. Furthermore, the expression patterns of HSP70 and cAPX were validated by western blot. Bioinformation analysis showed that the identified proteins were associated with a variety of functions, including energy and metabolism (30%), programmed cell death (9%), antioxidative processes (14%), and chaperonin (23%), secondary metabolism (3%), nitrogen metabolism (3%), cell growth/division (9), and other functional classes (9%).Of them, primary group in down-regulated expressed proteins were those involved in the energy and metabolism, which suggested that decreased energy and respiratory intermediate products might promote seed abortion in longan. The down-regulated APX might reduce the ability of antioxidant, under this condition, a possible increase in H2O2 concentration might occur, which seems to be a prerequisite factor for seed abortion in longan. And abortive seeds may have a lower ability to protein foldand protect because of down-regulated HSPs. Moreover, the up-regulated cysteine protease observed in abortive seeds may be a key event leading to the programmed death of these seeds.Our current study was aimed at characterizing differences between normal and abortive longan seeds at the proteome level. The study is the first close investigation, to our knowledge, on protein complement of longan seed abortion, and presents useful molecular information at protein level to further understand the mechanisms underlying logan seed abortion.