Molecular Evolution and Expression Divergence of the Aconitase (ACO) Gene Family in Land Plants

Abstract

Aconitase (ACO) is a key enzyme that catalyzes the isomerization of citrate to isocitrate in the tricarboxylic acid (TCA) and glyoxylate cycles. The function of ACOs has been well studied in model plants, such as Arabidopsis. In contrast, the evolutionary patterns of the ACO family in land plants are poorly understood. In this study, we systematically examined the molecular evolution and expression divergence of the ACO gene family in 12 land plant species. Thirty-six ACO genes were identified from the 12 land plant species representing the four major land plant lineages: Bryophytes, lycophytes, gymnosperms, and angiosperms. All of these ACOs belong to the cytosolic isoform. Three gene duplication events contributed to the expansion of the ACO family in angiosperms. The ancestor of angiosperms may have contained only one ACO gene. One gene duplication event split angiosperm ACOs into two distinct clades. Two clades showed a divergence in selective pressure and gene expression patterns. The cis-acting elements that function in light responsiveness were most abundant in the promoter region of the ACO genes, indicating that plant ACO genes might participate in light regulatory pathways. Our findings provide comprehensive insights into the ACO gene family in land plants.

Aconitase: To Be or not to Be Inside Plant Glyoxysomes, That Is the Question

“…However, they concluded that all land plant aconitases are cytosolic and no mitochondrial isoforms were present in the twelve genomes analyzed. This confirmed that a bioinformatics prediction should be treated with caution, as the conclusions of Wang et al [51] are not supported by the presence of The path of carbon in the glyoxylate cycle after van Roermund et al [46], Pracharoenwattana et al [49] and Pracharoenwattana and Smith [5]. Black arrows indicate glyoxylate cycle reactions up to sugars, while light blue arrows indicate the malate/oxaloacetate shuttle transport/reactions; the cytosolic enzymes are given in green, the glyoxysomal enzymes in blue, and the enzymes of the glyoxylate cycle including the cytosolic malate dehydrogenase are underlined.…”

“…However, they concluded that all land plant aconitases are cytosolic and no mitochondrial isoforms were present in the twelve genomes analyzed. This confirmed that a bioinformatics prediction should be treated with caution, as the conclusions of Wang et al [51] are not supported by the presence of aconitase activity and aconitase protein in mitochondrial fractions, as several authors previously found in different species both over 20 years ago [4,6,9,17,57] and more recently [58].…”

“…Thus, the enzyme aconitase appears to be present exclusively in the cytosol and the mitochondria (where part of the Krebs cycle is located). However, in the aconitase polypeptides specific targeting signals have not been identified, neither for peroxisomes [50] nor for mitochondria [51]. Thus, from these data it is not possible to distinguish genes encoding mitochondrial or cytosolic isoforms.…”

“…Few studies have focused on cytosolic and mitochondrial aconitase in other plants. Cots and Widmer [57] identified the soybean cytosolic aconitase participating in the glyoxylate cycle in the C1 isoform from the five aconitase isoforms identified in soybean seedlings (two mitochondrial: M1 and M2; three cytosolic: C1, C2 and C3), but six genes are expressed in Glycine max [51]. Eprintsev et al [61] identified one aconitase localized in the cytosol and one in the mitochondria of maize caryopses, with the former less inhibited by H 2 O 2 and possibly part of the glyoxylate cycle.…”

Polyamine and Ethylene pathways crosstalk revisited on a genome wide and gene function scale

“…Yet, a recent study indicated that SAM gene can function as a signaling molecule for ABA and H 2 O 2, and Medicago truncatula plants expressing MfSAM gene exhibited an improved cold tolerance while maintaining stable levels of polyamine and ethylene biosynthesis related genes activities [19]. Furthermore, Abscisic Acid Responsive Element (ABRE) cis-regulatory elements were found in both polyamine (SAMDC) [20] and ethylene (ACO) family genes [21] , and it was also shown in different plant species that a short term saline shock induces both polyamines and ethylene levels [22].…”