Glyoxylate rather than ascorbate is an efficient precursor for oxalate biosynthesis in rice

Area of Science:

• Plant biochemistry
• Molecular biology
• Agricultural science

Background:

• Oxalate is common in plants, with excess posing health risks.
• Its role in plant stress response and biosynthesis is debated.
• Understanding oxalate pathways is crucial for crop improvement.

Purpose of the Study:

• To identify the precursor and pathway for oxalate biosynthesis in plants.
• To investigate the role of glyoxylate and ascorbate in oxalate accumulation.
• To determine the relationship between oxalate and photorespiration.

Main Methods:

• Feeding experiments with glycolate and glyoxylate in detached rice leaves.
• Generation and analysis of transgenic rice plants with altered glyoxylate metabolism genes (SGAT, GGAT, HPR, ICL).
• Down-regulation of L-galactono-1,4-lactone dehydrogenase (GLDH) to study ascorbate's role.

Main Results:

• Glyoxylate and glycolate effectively stimulated oxalate accumulation.
• Cysteine inhibited glyoxylate-stimulated oxalate synthesis.
• Transgenic analyses confirmed glyoxylate as an efficient oxalate precursor in rice.
• Oxalate accumulation showed no correlation with photorespiration.
• Down-regulating GLDH did not affect oxalate levels despite reduced ascorbate.

Conclusions:

• Glyoxylate is the primary precursor for oxalate biosynthesis in rice.
• Oxalate accumulation is independent of photorespiration, possibly due to anaplerotic reactions.
• Ascorbate is not a direct precursor for oxalate synthesis in this context.