Differential expression and co‐regulation of carrot AOX genes (Daucus carota)

Abstract

Alternative oxidase (AOX) is a mitochondrial protein encoded by the nuclear genome. In higher plants AOX genes form a small multigene family mostly consisting of the two subfamilies AOX1 and AOX2. Daucus carota L. is characterized by a unique extension pattern of AOX genes. Different from other plant species studied so far it contains two genes in both subfamilies. Therefore, carrot was recently highlighted as an important model in AOX stress research to understand the evolutionary importance of both AOX subfamilies. Here we report on the expression patterns of DcAOX1a, DcAOX1b and DcAOX2a and DcAOX2b. Our results demonstrate that all of the four carrot AOX genes are expressed. Differential expression was observed in organs, tissues and during de novo induction of secondary root phloem explants to growth and development. DcAOX1a and DcAOX2a indicated a differential transcript accumulation but a similar co-expression pattern. The genes of each carrot AOX sub-family revealed a differential regulation and responsiveness. DcAOX2a indicated high inducibility in contrast to DcAOX2b, which generally revealed low transcript abundance and rather weak responses. In search for withingene sequence differences between both genes as a potential reason for the differential expression patterns, the structural organization of the two genes was compared. DcAOX2a and DcAOX2b showed high sequence similarity in their open reading frames (ORFs). However, length variability was observed in the N-terminal exon1 region. The predicted cleavage site of the mitochondrial targeting sequence in this locus is untypical small for both genes and consists of 35 amino acids for DcAOX2a and of 21 amino acids for DcAOX2b. The importance of structural gene organization and the relevancy of within-gene sequence variations are discussed. Our results strengthen the value of carrot as a model plant for future studies on the importance of AOX sub family evolution.

Alternative oxidase (AOX) and phenolic metabolism in methyl jasmonate-treated hairy root cultures of Daucus carota L.

“…In the present study, the DcAOX2a and DcAOX1a genes were chosen for correlation studies with phenylpropanoid biosynthesis because of known involvement of these two AOX genes in the process of developmental and cell reprogramming Frederico et al, 2009). Recently, Campos et al (2009) showed developmental and tissue specific differential transcript accumulation of DcAOX2a and DcAOX1a in D. carota. A parallel result was obtained in Arabidopsis thaliana, where AtAOX2 was differentially expressed during developmental stages (Clifton et al, 2006).…”

Cinnamate:CoA Ligase Initiates the Biosynthesis of a Benzoate-Derived Xanthone Phytoalexin in Hypericum calycinum Cell Cultures

“…Multiple sequence alignment was performed using the ClustalW platform in the BioEdit software (Campos et al, 2009). The alignment result was fit into MEGA 5.05 (Tamura et al, 2011) to construct a phylogenetic tree by the neighbor-joining method.…”

Alternative oxidase involvement in Daucus carota somatic embryogenesis

“…Recently, AOX genes have been isolated from D. carota (Campos et al 2009, Cardoso et al 2009, Costa et al 2009). The D. carota AOX ( DcAOX ) multigene family consists of two genes from the subfamily AOX1 and two genes from the subfamily AOX2 .…”

“…However, both genes of each subfamily demonstrated differential activities among each other. Typically, higher transcript accumulation and responsiveness were found for the two genes DcAOX1a and DcAOX2a and co‐regulation of both was demonstrated during de novo growth induction (Campos et al 2009).…”