Unveiling the Enigmatic Structure of TdCMO Transcripts in Durum Wheat

Durum wheat is one of the oldest and most important edible cereal crops and its cultivation has considerable economic importance in many countries. However, adverse conditions, such as high irradiance and increasing salinity of soils, could lead to a decrease in productivity over the next few decades. Durum wheat plants under salinityare able toaccumulate glycine betaine to osmotically balance the cytosol and reduce oxidative stress, especially in young tissues. However, the synthesis of this fundamental osmolyte is inhibited by high light in T. durum even under salinity. Choline monooxygenase is the first enzyme involved in the glycine betaine biosynthetic pathway. Thus, to explain the glycine betaine inhibition, we analyzed the effect of both salinity and high light on the putative TdCMO gene expression. Thirty-eight TdCMO different transcripts were isolated in the young leaves of durum wheat grown in different stress conditions. All translated amino acid sequences, except for the TdCMO1a6 clone, showed a frame shift caused by insertions or deletions. The presence of different transcripts could depend on the presence of duplicated genes, different allelic forms, and alternative splicing events. TdCMO1a6 computational modeling of the 3D structure showed that in durum wheat, a putative CMO-like enzyme with a different Rieske type motif, is present and could be responsible for the glycine betaine synthesis.

Choline monooxygenase transcript expression triggers glycine betaine accumulation in Suaeda maritima when subjected to a salt concentration optimal for its growth

Suaeda maritima(L.) Dumort, an annual halophyte known to be a salt-accumulator is also known for the accumulation of the osmolyte, glycine betaine (GB). This study is an attempt to understand the growth and GB accumulation under optimal concentration of 200 mM NaCl in S. maritima. Salt treatment with 200 mM NaCl showed a significant increase in shoot growth after two weeks. The shoots appeared succulent and turgid after two weeks of salt treatment compared to that of the control which appeared slender and wilted. The treated seedlings also exhibited a significant increase in GB content after two weeks of salt treatment. In order to determine the molecular basis of GB accumulation, qRT PCR of three key genes involved in the pathway, choline monooxygenase, betaine aldehyde dehydrogenase and phospho-ethanolamine N-methyl transferase was performed. Transcript level expression of the three genes revealed a high up-regulation of choline monooxygeanse transcripts when compared to that of the other two transcripts at two days of salt treatment. The results indicate that S. maritima requires salt for its growth and is a natural accumulator of GB. Although all the three genes were salt inducible, the high up-regulation of choline monooxygenase greatly contributes to the accumulation of GB under optimal growth as well as NaCl concentration.AbbreviationsBADHbetaine aldehyde dehydrogenaseCMOcholine monooxygenaseGBglycine betainePEAMTphosphoethanolamine N-methyl transferase

CMO1 encodes a putative choline monooxygenase and is required for the utilization of choline as the sole nitrogen source in the yeast Scheffersomyces stipitis (syn. Pichia stipitis)

Sixteen yeasts with sequenced genomes belonging to the ascomycete subphyla Saccharomycotina and Taphrinomycotina were assayed for their ability to utilize a variety of primary, secondary, tertiary and quartenary aliphatic amines as nitrogen sources. The results support a previously proposed pathway of quaternary amine catabolism whereby glycine betaine is first converted into choline, which is then cleaved to release trimethylamine, followed by stepwise demethylation of trimethylamine to release free ammonia. There were only a few instances of utilization of N-methylated glycine species (sarcosine and N,N-dimethylglycine), which suggests that this pathway is not intact in any of the species tested. The ability to utilize choline as a sole nitrogen source correlated strongly with the presence of a putative Rieske non-haem iron protein homologous to bacterial ring-hydroxylating oxygenases and plant choline monooxygenases. Deletion of the gene encoding the Rieske non-haem iron protein in the yeast Scheffersomyces stipitis abolished its ability to utilize choline as the sole nitrogen source, but did not affect its ability to use methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, ethanolamine or glycine as nitrogen sources. The gene was named CMO1 for putative choline monooxygenase 1. A bioinformatic survey of eukaryotic genomes showed that CMO1 homologues are found throughout the eukaryotic domain.