期刊
JOURNAL OF EXPERIMENTAL BOTANY
卷 69, 期 7, 页码 1649-1661出版社
OXFORD UNIV PRESS
DOI: 10.1093/jxb/erx483
关键词
Bornesitol; inositol methyltransferase; Litchi chinensis; osmotic stress; phloem transportation; quebrachitol
资金
- National Natural Science Fund of China [31471838]
- China Litchi and Longan Industry Technology Research System [CARS-33-11]
- Guangdong province science and technology plan projects [2016A020210063]
Although methylated cyclitols constitute a major proportion of the carbohydrates in many plant species, their physiological roles and biosynthetic pathway are largely unknown. Quebrachitol (2-O-methyl-chiro-inositol) is one of the major methylated cyclitols in some plant species. In litchi, quebrachitol represents approximately 50% of soluble sugars in mature leaves and 40% of the total sugars in phloem exudate. In the present study, we identified bornesitol as a transient methylated intermediate of quebrachitol and measured the concentrations of methyl-inositols in different tissues and in tissues subjected to different treatments. (CO2)-C-14 feeding and phloem exudate experiments demonstrated that quebrachitol is one of the transportable photosynthates. In contrast to other plant species, the biosynthesis of quebrachitol in litchi is not associated with osmotic stress. High quebrachitol concentrations in tissues of the woody plant litchi might represent a unique carbon metabolic strategy that maintains osmolality under reduced-sucrose conditions. The presence of bornesitol but not ononitol in the leaves indicates a different biosynthetic pathway with pinitol. The biosynthesis of quebrachitol involves the methylation of myo-inositol and the subsequent epimerization of bornesitol. An inositol methyltransferase gene (LcIMT1) responsible for bornesitol biosynthesis was isolated and characterized for the first time, and the biosynthesis pathways of methyl-inositols are discussed.
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