The Research Of GAPDH Gene Family’s Function In Banana Ripening

Banana (Musa spp.), one of the important fruits that is grown in tropical and subtropical regions, is also a significant food and cash crops in the world. It is a typical climacteric fruit, remarkably sensitive to ethylene. In the banana after-ripening process, the catabolism of glucose becomes rather active as the bioactivities of enzymes in starch synthesis intend to decrease, while bioactivities of decomposition-related enzymes increase, which causes most of the starches to be converted into soluble sugars. As has been known, GAPDH is not only a critical enzyme for glycolytic in banana after-ripening process, but also involved in processes like plant defense, anti-oxidation, protein interactions, plant hormone signaling and so no. And a preliminary study revealed that expression of GAPDH in banana peel could be up-regulated by ethylene induction. Since the ethylene has an important role in banana after-ripening process, it could help broaden our horizon for developing novel preservation techniques for banana to figure out the functions of GAPDH gene family in banana after-ripening process and its interactions with ethylene biosynthesis, ethylene signaling pathways and sugar signaling pathways.In this study, all the GAPDH gene family members were obtained and the evolutionary relationship studied through the retrieval of GAPDH gene family, which was carried out according to the information provided in banana genome databases. The expression characteristics of GAPDH gene family in banana members were also studied via semi-quantitative RT-PCR technique, taking Brazilian banana as the study objective. The transcriptional expressions of GAPDH in banana after-ripening post-processing under different treatments were studied afterward with QPCR techniques. The dynamic changes of fruit starch/glucose contents and GAPDH enzyme activities in pulp were measured in banana after-ripening post-processing. Detailed findings are as follows:1.18members of GAPDH gene family in banana were obtained according to the retrieval, of which the clone verifications were semiautomated. They were then categoried, according to their biochemical properties and subcellular localization, into GAPA/B、GAPCp、GAPC and NP-GAPDH groups, first three of which were phosphorylated GAPDH and located in the chloroplast, quality body and cytoplasm, respectively, while members of NP-GAPDH group are non-phosprorylated GAPDH and positioned in the cytoplasm. According to our research, the GAPA/B group has four members, named as MaGAPAl-2and MaGAPBl-2; and there is only one member in GAPCp group, called MaGAPCpl. The GAPC group has eleven members, designated as MaGAPC1-11, respectively, while there are two members in NP-GAPDH group named MaNP-GAPDH1and MaNP-GAPDH2.2. Bioinformatics analysis showed that N-terminal of GAPDH protein was low-conserved while its C-terminal highly-conserved. And there are two highly conserved domains in phosphorylated proteins MaGAPDH, Gp_dh_N and Gp_dh_C domains, while all the non-phosphorylated MaGAPDH proteins contained ALDH-F11domain. GAPDH gene families in banana are close to monocots rice, wheat Urartu and wheat in evolution, and distant with GAPDH in alfalfa and arabidopsis, indicating obvious monocots features.3. The expression analysis of MaGAPDH gene family in different tissues and organs of banana demonstrated that MaGAPA1/A2, MaGAPB1/B2and MaNP-GAPDH2were mainly expressed in leaves and fruits, the highest of which were in leaves; and that they were not detectable in roots and flowers. On the contrary, the expression of MaGAPC3were high in fruits, while the MaGAPC5/9was highly expressed in leaves, flowers and fruits and lowly expressed in roots. It also showed that MaGAPC7were mainly expressed in flowers and fruits, while lowly expressed in roots and leaves; MaGAPCl were expressed highest in the roots and leaves; MaGAPCpl, MaNP-GAPDH1and MaGAPC2/6/8/10/11could be detected in various tissues and organs, levels of which were consistent; and MaGAPC4was not detectable in roots, leaves, flowers and fruits.4. The expression patterns for different members of MaGAPDH gene family in banana after-ripening process differs from each other, showing the diversity of their functions. The detection showed that the expression trends of MaGAPCpl, MaGAPC5, MaGAPC9and MaGAPCTO was unimodal, which first increased and then reduced, while that of MaGAPCp3was obviously inhibited. It could also be seen the expression trends of MaGAPC6, MaNP-GAPDH1and MaNP-GAPDH2turned to fluctuate cyclically or irregularly. It could be speculated that some GAPDH members could be involved in glycolytic pathway, whose expression trends positively correlate with the energy supply in the fruit after-ripening process, while those whose expression trends fail to correlate with the energy supply might coupled with other ways and thus possessed different biological functions.5. According to the changes in the expression of genes related to ethylene synthesis and signal processing under the iodoacetic acid as well as the expression and enzymatic activity of MaGAPDH separately under bioEthephon/1-MCP treatment, it could be seen that expressions of MaACSl, MaACOl, MaERS2and MaERL3were inhibited during the absence of MaGAPDH, and that expressions of most MaGAPDH genes could be induced by ethylene while the enzymatic activity of MaGAPDH raised.6. In banana after-ripening process,the treatmentof iodoacetic acid inhibited the expression of MaHXKl and the processing of starch degradation fruit in peel, but enhanced the expression of MaHXKl in flesh. This showed that MaGAPDH facilitated the process of glucose metabolism. Neither the MaGAPDH expressions nor the MaGAPDH bioactivity was obviously inhibited or induced in fruits treated with of exogenous glucose, indicating that glucose wasn’t directly involved in a series of metabolic pathways which referred to GAPDH.7. It could be found in bananas treated with glucose that transcriptional expression of MaACSl, MaACO1, MaERS2and MaERL3within the banana peel were apparently inhibited, demonstrating that ethylene synthesis and signal transduction in banana peels could be inhibited by glucose, which also confirmed that the antagonism of glucose and ethylene signal existed in bananas, too.