Chloroplast Proteomics Analysis Of Low Temperature Stress Sugar Beet

In this study,the molecular mechanism of sugar beet chloroplast responding to chilling was explored at physiological,transcriptional and translation levels.The changes of relative electrolytic leakage and MDA content in different sugar beet materials during chilling were determined.The DREB family of sugar beet was analyzed by constructing maximum likelihood tree,and its expression pattern was identified by transcriptome sequencing and q RT-PCR.The changes of chloroplast proteome of sugar beet were determined by label free technique at 1 d after chilling.The results showed that KWS9442 has the strongest chilling resistance among 10 different sugar beet materials.The expression of Bv DREB reached to maximum at 1 d after chilling,implying activation of chilling response and cold acclimation.The proteomic analysis suggested that chloroplast thylakoid membrane,stroma and envelope are the main parts in response to chilling.On the chloroplast envelope,transporters were major chilling response proteins.They were mainly responsible for entrance and export of water,ions,sugars,proteins and other substances in chloroplast.Among them,the Toc-Tic complex may preferentially transport photosystem proteins into chloroplasts under the guidance of Bv LTD and benefit for photosynthesis in sugar beet under low temperature.In the chloroplast stroma,chilling response proteins were mainly involved in the Calvin cycle,pentose phosphate pathway and starch synthesis and metabolism.The expression changes of Bv ISA3,Bv PU1,Bv GWD3,which were participated in starch synthesis and metabolism,were related to the formation of chloroplast starch granules.In addition,significantly changes of 50 S and 30 S ribosomal proteins were also detected in the stroma.It is indicated that proteins were translated from chloroplast DNA in response to chilling for maintaining photosynthesis.A large number of photosynthetic proteins in chloroplast thylakoid membrane were responding to chilling,including 13 up-regulated proteins.Especially,the change fold of the alpha subunit of ATP synthase reached to 23 times.Several proteins involved in reactive oxygen species(ROS)scavenging were also detected in the chloroplast thylakoid membrane and stroma.Besides ROS scavenging pathways consist of Bv Cu/Zn-SOD and Bv CAT,peroxiredoxin(Prx)and thioredoxin(Trx)also played important roles in chloroplast ROS scavenging.Prx and Trx also played important role in activating the H2O2 signaling pathway and inducing resistance-related gene expression.On the basis of above results and related literatures,schematic presentation of chilling response and cold acclimation mechanisms in chloroplast of sugar beet was concluded.It provides theoretical basis for breeding chilling tolerant sugar beet varieties.