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Plants (Basel). 2019 May 14;8(5). pii: E126. doi: 10.3390/plants8050126.

Common Bean (Phaseolus vulgaris L.) Accumulates Most S-Methylcysteine as Its γ-Glutamyl Dipeptide.

Author information

1
Genomics and Biotechnology, London Research and Development Centre, Agriculture and Agri-Food Canada, London, ON N5V 4T3, Canada. saboorielham@gmail.com.
2
Department of Plant Breeding and Biotechnology, Faculty of Agriculture, University of Zabol, Zabol 538-98615, Iran. saboorielham@gmail.com.
3
Genomics and Biotechnology, London Research and Development Centre, Agriculture and Agri-Food Canada, London, ON N5V 4T3, Canada. jayajoshi20@gmail.com.
4
Department of Biology, University of Western Ontario, London, ON N6A 3K7, Canada. jayajoshi20@gmail.com.
5
Horticultural Sciences Department, University of Florida, Gainesville, FL 32611, USA. jayajoshi20@gmail.com.
6
Genomics and Biotechnology, London Research and Development Centre, Agriculture and Agri-Food Canada, London, ON N5V 4T3, Canada. Aga.Pajak@canada.ca.
7
Department of Plant Breeding and Biotechnology, Faculty of Agriculture, University of Zabol, Zabol 538-98615, Iran. mahmood.solouki@uoz.ac.ir.
8
Agricultural Biotechnology Research Institute of Iran (ABRII), Agricultural Research Education and Extension Organization (AREEO), Karaj 31585-845, Iran. mthrhm@abrii.ac.ir.
9
Genomics and Biotechnology, London Research and Development Centre, Agriculture and Agri-Food Canada, London, ON N5V 4T3, Canada. Justin.Renaud@canada.ca.
10
Genomics and Biotechnology, London Research and Development Centre, Agriculture and Agri-Food Canada, London, ON N5V 4T3, Canada. Frederic.Marsolais@canada.ca.
11
Department of Biology, University of Western Ontario, London, ON N6A 3K7, Canada. Frederic.Marsolais@canada.ca.

Abstract

The common bean (Phaseolus vulgaris) constitutes an excellent source of vegetable dietary protein. However, there are sub-optimal levels of the essential amino acids, methionine and cysteine. On the other hand, P. vulgaris accumulates large amounts of the γ-glutamyl dipeptide of S-methylcysteine, and lower levels of free S-methylcysteine and S-methylhomoglutathione. Past results suggest two distinct metabolite pools. Free S-methylcysteine levels are high at the beginning of seed development and decline at mid-maturation, while there is a biphasic accumulation of γ-glutamyl-S-methylcysteine, at early cotyledon and maturation stages. A possible model involves the formation of S-methylcysteine by cysteine synthase from O-acetylserine and methanethiol, whereas the majority of γ-glutamyl-S-methylcysteine may arise from S-methylhomoglutathione. Metabolite profiling during development and in genotypes differing in total S-methylcysteine accumulation showed that γ-glutamyl-S-methylcysteine accounts for most of the total S-methylcysteine in mature seed. Profiling of transcripts for candidate biosynthetic genes indicated that BSAS4;1 expression is correlated with both the developmental timing and levels of free S-methylcysteine accumulated, while homoglutathione synthetase (hGS) expression was correlated with the levels of γ-glutamyl-S-methylcysteine. Analysis of S-methylated phytochelatins by liquid chromatography and high resolution tandem mass spectrometry revealed only small amounts of homophytochelatin-2 with a single S-methylcysteine. The mitochondrial localization of phytochelatin synthase 2-predominant in seed, determined by confocal microscopy of a fusion with the yellow fluorescent protein-and its spatial separation from S-methylhomoglutathione may explain the lack of significant accumulation of S-methylated phytochelatins.

KEYWORDS:

Phaseolus vulgaris; S-methylcysteine; common bean; cysteine; homoglutathione; methionine; phytochelatin synthase

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