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Title: Isolation and characterization of the aconitate hydratase 4 (Aco4) gene from soybean

Author
item COLEMAN, ZACHARY - University Of Wisconsin
item BOELTER, JESSICA - Iowa State University
item ESPINOSA, KATHERINE - Iowa State University
item GOGGI, SUSANA - Iowa State University
item PALMER, REID - Iowa State University
item Sandhu, Devinder

Submitted to: Canadian Journal of Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2017
Publication Date: 2/2/2017
Citation: Coleman, Z., Boelter, J., Espinosa, K., Goggi, S., Palmer, R.G., Sandhu, D. 2017. Isolation and characterization of the aconitate hydratase 4 (Aco4) gene from soybean. Canadian Journal of Plant Science. 97(4):648-691. doi: 10.1139/CJPS-2016-0363.

Interpretive Summary: Cellular respiration is the process of converting the chemical energy stored in food into ATP for all energy consuming activities of the cell. Aconitase is an important enzyme that is critical for cellular respiration. Five aconitase genes namely Aco1, Aco2, Aco3, Aco4 and Aco5 have been identified in soybean. In our previous work we have genetically mapped Aco4 on chromosome 11. The purpose of this investigation was to isolate and sequence the candidate gene for Aco4. We mapped the Aco4 gene to a 148 kb region on chromosome 11 that contained 19 putative genes. One of these, Glyma.11G080600 is predicted to code for the aconitase enzyme. Sequencing of Glyma.11G080600 for two aconitase variants (A-line and B-line) revealed two changes at the amino acid level that caused different protein structure in the variant lines. Structure of the Glyma.11G080600 protein was consistent with its function during cellular respiration. Evolutionary analysis showed that Aco4 is closely associated gene to Aco1 in soybean and may have developed during a recent duplication event. Functional characterization of the Aco4 gene puts new light on our understanding of the respiration process. Findings of this investigation will be valuable to plant physiologists, geneticists and plant breeders in manipulating cellular respiration for efficient utilization of resources by plants to achieve higher productivity.

Technical Abstract: Aconitase catalyzes the reversible isomerization of two tricarboxylic acids citrate and isocitrate during the Krebs cycle. Five aconitase genes namely Aco1, Aco2, Aco3, Aco4 and Aco5 have been identified in soybean. Previously, Aco4 was mapped on chromosome 11. The purpose of this investigation was to isolate and sequence the candidate gene for Aco4. We mapped the Aco4 gene to a 148 kb region on chromosome 11 that contained 19 predicted genes. One of these, Glyma.11G080600, codes for aconitate hydratase. Sequencing of two isozyme variants for Glyma.11G080600 revealed three synonymous and two non-synonymous substitutions. Perhaps, the two non-synonymous substitutions resulted in a variable isozyme pattern between A-line and B-line. Glyma.11G080600 contains a catalytic domain and a swivel domain that are known to catalyze isomerization of citrate to isocitrate and swiveling conformational change in the enzyme mechanism, respectively. Conservation of both the domains signifies that Glyma.11G080600 is able to catalyze the interconversion of citrate and isocitrate. Glyma.11G080600 is expressed in most plant tissues with maximum expression in leaves. Phylogenetic analysis of 25 genes from different species showed three major clusters. Glyma.11G080600 (Aco4) and Glyma.01G162800 that are conserved in Glycine max and G. soja may have common ancestry before G. max and G. soja split.