Expression of Xhdsi-1VOC, a novel member of the vicinal oxygen chelate (VOC) metalloenzyme superfamily, is up-regulated in leaves and roots during desiccation in the resurrection plant Xerophyta humilis (Bak) Dur and Schinz

Abstract

The annotation of novel plant genes is frequently based on sequence and structural similarity to known protein motifs. Understanding the biological function of these genes is dependent on identifying conditions under which they are activated, however. The resurrection plant, Xerophyta humilis is a good model system for identifying and characterizing genes which are important for desiccation tolerance. Desiccation induced-1 (dsi-1VOC), a previously uncharacterized plant gene, is up-regulated during desiccation in leaves, roots, and seeds in X. humilis. The X. humilis desiccation induced-1 gene, Xhdsi-1VOC, shares structural homology with the vicinal oxygen chelate (VOC) metalloenzyme superfamily. Proteins in this superfamily share little sequence similarity, but are characterized by a common βαβββ structural fold. A number of plant orthologues of XhDsi-1VOC have been identified, including Arabidopsis thaliana At1g07645, which is currently annotated as a glyoxalase I-like gene, and many ESTs derived from seed cDNA libraries. Xhdsi-1VOC and its orthologues do not, however, contain the glutathione and zinc binding sites conserved in glyoxalase I genes. Furthermore, expression of Xhdsi-1VOC in yeast failed to rescue a yeast glyoxalase I mutant. Messenger RNA transcripts for At1g07645 accumulate during seed maturation, but are not induced by water loss, salt or mannitol stress in vegetative tissue in Arabidopsis. It is concluded that dsi-1VOC is a seed-specific gene in desiccation-sensitive plants that is activated by water loss in vegetative tissues in the resurrection plant X. humilis and plays an important role in allowing plant tissues to survive loss of 95% of their relative water content.

Whole-Genome Identification and Expression Pattern of the Vicinal Oxygen Chelate Family in Rapeseed (Brassica napus L.)

“…Because homologous VOC genes were mainly related to desiccation and drought stress, there are fewer reports regarding their function under other types of abiotic stress (Mulako et al, 2008; Mustafiz et al, 2014). B. napus were treated with drought stress to study the BnaVOC expression pattern under drought stress conditions; to determine whether the BnaVOC s expression is linked to lipid formation under drought condition, high oil content and low oil content B. napus were used, and the analysis was performed with qPCR analysis.…”

The use of aeroponics to investigate antioxidant activity in the roots of Xerophyta viscosa

“…Importantly, however, all the antioxidant enzymes were able to maintain activity when extracted from tissues with RWC 10%. This has been reported to be the case in leaves of this and other resurrection plants such as Xerophyta humilis, Eragrostis nindensis, Craterostigma wilmsii and Myrothanmus flabellifolius and is believed to be important in quenching of ROS in recovery of metabolism upon rehydration; the same enzymes being used during rehydration rather than reliance on de novo synthesis of enzymes occurring once full hydration is achieved (Farrant 2000(Farrant , 2007Mowla et al 2002;Illing et al 2005;Mulako et al 2008). While our data indicate that a decline (or relative maintenance) in extent of enzyme activity occurs during drying in roots of X. viscosa, the opposite is true in leaves …”

“…We report here on use of such a system to study the effects of desiccation on roots of this resurrection plant. One of the key protective mechanisms induced during desiccation involves the upregulation of antioxidant activity (Farrant 2000(Farrant , 2007Mowla et al 2002;Moore et al 2004;Kranner and Birtic 2005;Illing et al 2005;Moore et al 2009;Mulako et al 2008). This involves the ''classical'' (Kranner and Birtic 2005) or ''housekeeping'' antioxidants (Illing et al 2005), so called because they are present in all plants and are crucial to maintenance of cellular homeostasis under dayto-day conditions and in protection against a myriad of abiotic and biotic stresses (for an overview, see Estner and Oswald, 1994).…”

“…The key difference between desiccationtolerant (DT) and-sensitive (DS) plants appears to be the ability to maintain such antioxidant potential in the dry state such that the same can be utilized during rehydration and thus protect against the ROS stress associated with reconstitution of full metabolism (reviewed in Farrant 2007;Moore et al 2009). In addition, resurrection plants have the ability to induce, de novo, antioxidants such as 1-and 2-cys-peroxiredoxins, glyoxylase I family proteins, zinc metallothionine and metallothionine-like antioxidants (Blomstedt et al 1998;Mowla et al 2002;Collett et al 2004;Illing et al 2005;Farrant et al 2007;Mulako et al 2008) that have been reported to be important in DT of orthodox seeds but are never found to be upregulated in their (DS) vegetative tissues (Aalen 1999;Stacey et al 1999). In this study we investigated the role of some of the key housekeeping antioxidants during drying of roots of X. viscosa.…”

Topological variation in the evolution of new reactions in functionally diverse enzyme superfamilies

“…Still, it is intriguing to speculate that the variant topology represented by these two proteins is likely to play a role. Other new extradiol dioxygenases have been recently identified that may represent yet additional topological variants evolved to accommodate functional requirements via mixing and matching of subdomain modules [24,25]. …”