Aox gene structure, transcript variation and expression in plants

Abstract

Alternative oxidase (Aox) has been proposed as a functional marker for breeding stress tolerant plant varieties. This requires presence of polymorphic Aox allele sequences in plants that affect plant phenotype in a recognizable way. In this review, we examine the hypothesis that organization of genomic Aox sequences and gene expression patterns are highly variable in relation to the possibility that such a variation may allow development of Aox functional markers in plants. Aox is encoded by a small multigene family, typically with four to five members in higher plants. The predominant structure of genomic Aox sequences is that of four exons interrupted by three introns at well conserved positions. Evolutionary intron loss and gain has resulted in the variation of intron numbers in some Aox members that may harbor two to four introns and three to five exons in their sequence. Accumulating evidence suggests that Aox gene structure is polymorphic enough to allow development of Aox markers in many plant species. However, the functional significance of Aox structural variation has not been examined exhaustively. Aox expression patterns display variability and typically Aox genes fall into two discrete subfamilies, Aox1 and Aox2, the former being present in all plants and the latter restricted in eudicot species. Typically, although not exclusively, the Aox1-type genes are induced by many different kinds of stress, whereas Aox2-type genes are expressed in a constitutive or developmentally regulated way. Specific Aox alleles are among the first and most intensively stressinduced genes in several experimental systems involving oxidative stress. Differential response of Aox genes to stress may provide a flexible plan of plant defense where an energy-dissipating system in mitochondria is involved. Evidence to link structural variation and differential allele expression patterns is scarce. Much research is still required to understand the significance of polymorphisms within AOX gene sequences for gene regulation and its potential for breeding on important agronomic traits. Association studies and mapping approaches will be helpful to advance future perspectives for application more efficiently.

Overexpression of an alternative oxidase gene, OsAOX1a, improves cold tolerance in Oryza sativa L.

“…It is well documented that AOX1s could be induced by various biotic and abiotic stresses, whereas AOX2 is usually developmentally expressed and constitutively regulated by environmental factors (Polidoros et al, 2009). Many studies have indicated that the lack of AOX1 reduces the tolerance or growth ability under stress.…”

Alternative Oxidase Isoforms Are Differentially Activated by Tricarboxylic Acid Cycle Intermediates

“…Studies on various transgenic plants indicate that these isoforms are not redundant and cannot compensate for each other under stress or adverse growth conditions (Table I). These include studies on Arabidopsis (Arabidopsis thaliana), which has five nuclear AOX genes: four AOX1 type (A-D) and one AOX2 type (Polidoros et al, 2009). In Arabidopsis, an aox1a knockout cannot be compensated by the expression of other isogenes (Table I; Strodtkötter et al, 2009;Kühn et al, 2015).…”

Plant respiration under low oxygen

“…In plants, it is possible for electron transport to O 2 to occur in the presence of light through thylakoidal membranes of chloroplasts, via chlororespiration (Figure 3) (Polidoros et al, 2009), distinct from photorespiration (Bennoun, 1982;Peltier and Cournac, 2002) and the Mehler reaction. The function of this process is to ensure supplies of ATP and NAD(P)H generated by glycolysis for converting starch into triose phosphate (D-glyceraldehyde phosphate or dihydroxyacetone phosphate) (Bauwe et al, 2010;Maurino and Peterhansel, 2010).…”

“…Studies have elucidated a crucial role of AOX in protecting against ROS produced during oxidative stress (van Dongen et al, 2011), and it can also influence mitochondrial adaptability to different kinds of stress (Moller, 2001;Rasmusson et al, 2009), even expressing mitochondrial genes in a wide variety of environments. AOX acts against ROS as follows: AOX allows electron transfer from ubiquinone (UQ) to O 2 , which high levels of reducing agents in the UQ pool can be dissipated through AOX, thus avoiding the formation of ROS (Polidoros et al, 2009). …”