Arabidopsis prolyl 4-hydroxylases are differentially expressed in response to hypoxia, anoxia and mechanical wounding

Prolyl 4-hydroxylases (P4H; EC 1.14.11.2) have been studied extensively in various organisms and recently in relation to oxygen deficiency while little is known about their role in response to similar stresses in plants. To this direction, we investigated the expression patterns of Arabidopsis P4Hs under hypoxia, anoxia and mechanical wounding. The 13 Arabidopsis P4Hs are low-abundance transcripts with differential patterns of expression in response to two hypoxic, 1.5% and 5% O-2, anoxic conditions and mechanical wounding. The majority of AtP4Hs showed higher levels of expression in roots compared with shoots under hypoxia and anoxia. Hypoxia of 1.5% O-2 induced the expression of six AtP4Hs, while hypoxia of 5% O-2 and anoxia induced the expression of three and two AtP4Hs, respectively. Moreover, we identified in silico, 308 Arabidopsis genes among the differentially expressed genes under hypoxia that contain proline hydroxylation motifs. It is likely that the AtP4Hs hydroxylate proline residue(s) of the 308 polypeptides suggest involvement in their post-translational modification process. This modification might serve as an alternative level of regulation for the function of these polypeptides in the context of hypoxic response. Furthermore, six AtP4Hs were upregulated in response to mechanical wounding, suggesting involvement in this stress response.