Abstract
The red seaweed Pyropia yezoensis is an ideal research model for dissecting the molecular mechanisms underlying its robust acclimation to abiotic stresses in intertidal zones. Glycine betaine (GB) was an important osmolyte in maintaining osmotic balance and stabilizing the quaternary structure of complex proteins under abiotic stresses (drought, salinity, etc.) in plants, animals, and bacteria. However, the existence and possible functions of GB in Pyropia remain elusive. In this study, we observed the rapid accumulation of GB in desiccated Pyropia blades, identifying its essential roles in protecting Pyropia cells against severe osmotic stress. Based on the available genomic and transcriptomic information of Pyropia, we computationally identified genes encoding the three key enzymes in the GB biosynthesis pathway: phosphoethanolamine N-methyltransferase (PEAMT), choline dehydrogenase (CDH), and betaine aldehyde dehydrogenase (BADH). Pyropia had an extraordinarily expanded gene copy number of CDH (up to seven) compared to other red algae. Phylogeny analysis revealed that in addition to the one conservative CDH in red algae, the other six might have originated from early gene duplication events. In dehydration stress, multiple CDH paralogs and PEAMT genes were coordinating up-regulated and shunted metabolic flux into GB biosynthesis. An elaborate molecular mechanism might be involved in the transcriptional regulation of these genes.
Highlights
Plant performance and yield responses to water deficit stress conditions have been extensively studied [1,2,3]
What are the roles of the Glycine betaine (GB) in response to osmotic stress in Pyropia? What influences the diversity and conservation of the GB biosynthesis pathway in Pyropia? To address these questions, in this study, we computationally identified genes involved in the betaine biosynthesis pathway
To determine whether GB exists in red seaweed P. yezoensis and whether it is involved in desiccation tolerance, we detected the amounts of GB in the dehydration process
Summary
Plant performance and yield responses to water deficit stress conditions have been extensively studied [1,2,3]. Water deficiency causes cell metabolic disorder and cell membrane mechanical damage. A decline in leaf relative water content (RWC) reflects a loss of turgor that results in limited cell expansion and thereby reduced growth in crop plants [4,5]. (N,N,N-trimethylglycine) is a quaternary ammonium compound found in bacteria, halophilic archaebacteria, marine invertebrates, plants, and mammals [6,7,8,9]. GB can maintain the osmotic balance and stabilize the quaternary structure of complex proteins under abiotic stresses. Treating plants with exogenous GB or increasing GB content in transgenic plants would greatly enhance their tolerance
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