Genome-wide Analysis Of The Fructose Bisphosphate Aldolases In Arabidopsis

Fructose bisphosphate aldolase (EC 4.1.2.13), simply called aldolase, catalyzes the reversible cleavage of fructose 1, 6-biphosphate into two triose sugars, glyceroldhyde 3-phosphate (G-3-P) and dihydroxyacetone-phosphate (DHAP). It is a constituent of both the glycolytic/gluconeogenic pathway and the pentose phosphate cycle. In plant, there are two isoforms of aldolases are different in the primary structure and subcellular localization: chloroplasts and cytosol and they are encoded by partly homologous genes.Fructose 1, 6-bisphospate could be futher metabolized to fructose, glucose and sucrose. Sugar signal transduction played a particular role in the ethylene and ABA signal transduction. A large number of stress responsive genes were also induced by glucose, indicating a role of sugar in environmental responses. Meanwhile, a few transcriptomic and proteomics experiments suggested that aldolases may response to abiotic stresses or hormones in Arabidopsis. During the past few years, great quantity of researches had been done on aldolases in various organisms, which mainly focused at physiological and biochemical level. To date, it is poorly known about the cellular and developmental processes of which aldolses are required, and how their activity is regulated by hormone and environmental stimuli in Arabidopsis thaliana. The main results were as follows:(1) The Arabidopsis genome encodes at least 8 FBA-like aldolase proteins which could be divided into two subfamilies, and within each subfamily AtFBAs show similar gene structures and protein structures. AtFBAs distribute on chromosome 2-5. AtFBA1-AtFBA2 and AtFBA4-AtFBA8 are duplicated gene pairs.(2) We predicted their subcelluar location of AtFBAs. AtFBA1, AtFBA2, AtFBA3 imported into plastid, while AtFBA4 might mitochondrion. The other four had no location data, which is located in cytosol.(3) We employed a quantitative RT-PCR approach to detect the mRNA accumulations of each AtFBAs in root, rosette leaf, cauline leaf, stem, and flower. The results showed that the majority of genes displayed tissue-specific expression patterns. Only AtFBA6 was constitutively expressed in different tissues with a similar level. The transcripts of AtFBA1, AtFBA2, AtFBA5 and AtFBA7 were accumulated much in shoot but not root; AtFBA4 and AtFBA8 were detected in similar expression pattern they much in flower and a little in other tissues; AtFBA3 was the only member which mainly resided in root.(4) Treated with glucose and fructose, the transcriptional enhancement or reduction was observed in some members. The treatment of glucose varied the mRNA of AtFBA2, AtFBA6, AtFBA7 and AtFBA8 to accumulated, while fructose AtFBA1, AtFBA3, AtFBA5, AtFBA6 and AtFBA8. AtFBA6 was suppressed and AtFBA8 was induced by glucose and fructose respectively, while AtFBA4 could not be respond to any sugar.(5) We examined AtFBAs expression levels under different hormonal or environmental conditions, such as NaCl, oxidative stress, osmotic stress, high temperature, low temperatures, cadmium, ABA and SA, by quantitative RT-PCR analysis. The mRNA levels of most AtFBAs were regulated by hormonal or environmental treatments. For shoot, during the SA, NaCl, Cd and drought treatment, all the members were significantly affected which suggested that all the aldoses take part in defense, salt stress and heavy-metal stress signal pathways. AtFBA1, AtFBA3, AtFBA6 and AtFBA8 induced by hormonal stimuli. Except for AtFBA1, the transcriptional enhancement or reduction of aldolases was observed in shoot of Arabidopsis seedlings which subjected to stress treatments of 4?C and 37?C. When treated with UV-B light, the transcriptional enhancement of AtFBA3, AtFBA6 and AtFBA8 was detected more than 10-folds as much as control. For root, AtFBA3 was strongly repressed by all the treatments and AtFBA4 responded stronger than shoot.(6) In order to characterize AtFBAs, we constructed overexpression and got the knockout mutants of some members from SALK. Compare with wide type, fba2 exhibited smaller. Meanwhile, AtFBA6-overexpressing Arabidopsis plants showed phenotype of smaller, abnormal leaf and highly sensitive to salt stress.