Characterization of a Functional Role of the Bradyrhizobium japonicum Isocitrate Lyase in Desiccation Tolerance

Abstract

Bradyrhizobium japonicum is a nitrogen-fixing symbiont of soybean. In previous studies, transcriptomic profiling of B. japonicum USDA110, grown under various environmental conditions, revealed the highly induced gene aceA, encoding isocitrate lyase (ICL). The ICL catalyzes the conversion of isocitrate to succinate and glyoxylate in the glyoxylate bypass of the TCA cycle. Here, we evaluated the functional role of B. japonicum ICL under desiccation-induced stress conditions. We purified AceA (molecular mass = 65 kDa) from B. japonicum USDA110, using a His-tag and Ni-NTA column approach, and confirmed its ICL enzyme activity. The aceA mutant showed higher sensitivity to desiccation stress (27% relative humidity (RH)), compared to the wild type. ICL activity of the wild type strain increased approximately 2.5-fold upon exposure to 27% RH for 24 h. The aceA mutant also showed an increased susceptibility to salt stress. Gene expression analysis of aceA using qRT-PCR revealed a 148-fold induction by desiccation, while other genes involved in the glyoxylate pathway were not differentially expressed in this condition. Transcriptome analyses revealed that stress-related genes, such as chaperones, were upregulated in the wild-type under desiccating conditions, even though fold induction was not dramatic (ca. 1.5–2.5-fold).

Alternative fate of glyoxylate during acetate and hexadecane metabolism in Acinetobacter oleivorans DR1

“…In the β-oxidation cycle, inhibition of FadR by fatty acids inactivates the aceA repressor, IclR, inducing expression of the aceBAK operon, whose products convert isocitrate to malate through the GS cycle in Escherichia coli 1,2 . The GS is also a main carbon flux under several stress conditions, such as oxidative stress, antibiotic stress, cold-/heat-shock, and even desiccation 3–5 . Although the detailed mechanism of the activated GS pathway under conditions of stress is not well studied, it could avoid unnecessary ROS generation by bypassing NADH/FADH production, and respiration, eventually helping cells to survive in harsh conditions 6 .…”

The PEG-responding desiccome of the alder microsymbiont Frankia alni

“…Strategies adopted by these microorganisms for desiccation tolerance include prevention of ROS damage, osmoprotection through the accumulation of sucrose and/or trehalose 10 , 22 , the uptake of exogenous glycine betaine 23 , the production of extracellular polysaccharides (EPS) that reduce water loss 24 , or the ability to limit protein oxidation during dehydration 21 . Previous studies 8 , 20 , 21 , 25 – 27 highlighted changes in expression of several genes following water stress including genes for synthesis of trehalose/sucrose, sugar transporters, chaperone genes ( groES / EL , dnaK / J ), oxidative stress protection genes ( dps , thioredoxin), ABC transporters, dehydrogenases, esterases, proteases, hydrolases and lyases. A Casuarina -infective Frankia strain was recently shown to have few proteins upregulated under salt stress, among which cell wall/membrane biogenesis functions and some transport proteins 13 .…”

WITHDRAWN: Deep expression scrutiny provides genetic basis of aluminium tolerance in wild (Lens nigrican) and cultivated lentil (Lens culinaris Medik.)

“…Isocitrate lyase is an enzyme of the glyoxylate cycle which accelerates the cleavage of isocitrate to succinate and glyoxylate. Bradyrhizobium japonicum isocitrate lyase has been reported to have an important functional role in desiccation tolerance[50]. Poly(C)-binding proteins (PCBPs) PCBPs might itself be standardized by their localization within the cell and it can work as a signal-dependent and coordinated regulator of transcription in eukaryotic cells.…”