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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% O2, 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% O2 induced the expression of six AtP4Hs, while hypoxia of 5% O2 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.

Prolyl 4-hydroxylases (P4Hs) catalyze the proline hydroxylation, a major post-translational modification, of hydroxyproline-rich glycoproteins. Two carnation petal P4H cDNAs, (Dianthus caryophyllus prolyl 4-hydroxylase) DcP4H1 and DcP4H2, were identified and characterized at the gene expression and biochemical level in order to investigate their role in flower senescence. Both mRNAs showed similar patterns of expression with stable transcript abundance during senescence progression and differential tissue-specific expression with DcP4H1 and DcP4H2 strongly expressed in ovaries and stems, respectively. Recombinant DcP4H1 and DcP4H2 proteins were produced and their catalytic properties were determined. Pyridine 2,4-dicarboxylate (PDCA) was identified as a potent inhibitor of the in vitro enzyme activity of both P4Hs and used to determine whether inhibition of proline hydroxylation in petals is involved in senescence progression of cut carnation flowers. PDCA suppressed the climacteric ethylene production indicating a strong correlation between the inhibition of DcP4H1 and DcP4H2 activity in vitro by PDCA and the suppression of climacteric ethylene production in cut carnation flowers.

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Olive (Olea europaea L.) is one of the most important crops in the Mediterranean region. The expansion of cultivation in areas irrigated with low quality and saline water has negative effects on growth and productivity however the investigation of the molecular basis of salt tolerance in olive trees has been only recently initiated. To this end, we investigated the molecular response of cultivar Kalamon to salinity stress using next-generation sequencing technology to explore the transcriptome profile of olive leaves and roots and identify differentially expressed genes that are related to salt tolerance response. Out of 291,958 obtained trimmed reads, 28,270 unique transcripts were identified of which 35% are annotated, a percentage that is comparable to similar reports on non-model plants. Among the 1,624 clusters in roots that comprise more than one read, 24 were differentially expressed comprising 9 down- and 15 up-regulated genes. Respectively, inleaves, among the 2,642 clusters, 70 were identified as differentially expressed, with 14 down- and 56 up-regulated genes. Using next-generation sequencing technology we were able to identify salt-response-related transcripts. Furthermore we provide an annotated transcriptome of olive as well as expression data, which are both significant tools for further molecular studies in olive.