Identification of an additional protein involved in mannan biosynthesis. (19th October 2012)

• Record Type: Journal Article
• Authors: Wang, Yan; Mortimer, Jennifer C.; Davis, Jonathan; Dupree, Paul; Keegstra, Kenneth
• Is Part Of: Plant journal. Volume 73:Number 1(2013:Jan.)
• Page Start: 105
• Page End: 117
• Publication Date: 2012-10-19
• Subjects: Plant molecular biology -- Periodicals; Plant cells and tissues -- Periodicals; Botany -- Periodicals; 580
• DOI: 10.1111/tpj.12019
• Languages: English
• ISSNs: 0960-7412

Abstract

<abstract abstract-type="main" id="tpj12019-abs-0001"> <title>Summary</title> <p>Galactomannans comprise a β‐1, 4‐mannan backbone substituted with α‐1, 6‐galactosyl residues. Genes encoding the enzymes that are primarily responsible for backbone synthesis and side‐chain addition of galactomannans were previously identified and characterized. To identify additional genes involved in galactomannan biosynthesis, we previously performed deep EST profiling of fenugreek (<italic>Trigonella foenum</italic>‐<italic>graecum </italic>L.) seed endosperm, which accumulates large quantities of galactomannans as a reserve carbohydrate during seed development. One of the candidate genes encodes a protein that is likely to be a glycosyltransferase. Because this protein is involved in mannan biosynthesis, we named it 'mannan synthesis‐related' (MSR). Here, we report the characterization of a fenugreek <italic>MSR</italic> gene (<italic>TfMSR</italic>) and its two Arabidopsis homologs, <italic>AtMSR1</italic> and <italic>AtMSR2</italic>. <italic>TfMSR</italic> was highly and specifically expressed in the endosperm. TfMSR, AtMSR1 and AtMSR2 proteins were all determined to be localized to the Golgi by fluorescence confocal microscopy. The level of mannosyl residues in stem glucomannans decreased by approximately 40% for Arabidopsis <italic>msr1</italic> single T‐DNA insertion mutants and by more than 50% for <italic>msr1 msr2</italic> double mutants, but remained unchanged for <italic>msr2</italic> single mutants. In addition, <italic>in vitro</italic> mannan synthase activity from the stems of <italic>msr1</italic> single and <italic>msr1 msr2</italic> double mutants also decreased. Expression of <italic>AtMSR1</italic> or <italic>AtMSR2</italic> in the <italic>msr1 msr2</italic> double mutant completely or partially restored mannosyl levels. From these results, we conclude that the MSR protein is important for mannan biosynthesis, and offer some ideas about its role.</p> </abstract>