Unraveling the malate biosynthesis during development of <i>Torreya grandis</i> nuts

Abstract

<i>Torreya grandis</i> is a characteristic rare economic tree species in subtropical mountainous areas. The kernels of <i>T. grandis</i> have rich content of organic acids, and malate is the predominant organic acid in <i>T. grandis</i> kernels. However, the contents, biosynthesis/metabolism pathway and transcriptional regulation of malate in developing <i>T. grandis</i> kernels remain completely unknown. Here, the organic acid composition in developing <i>T. grandis</i> kernels was first analyzed. The results showed that the content of malate was increased during the maturation <i>T. grandis</i> kernels. A malate synthase (TgMLS) gene might be involved in the accumulation of malate based on transcriptome data, gene expression and enzyme activity analysis. Transient expression of <i>TgMLS</i> in tobacco resulted in the high malate synthase activity and malate content. Furthermore, a basic helix-loop-helix transcription factor (bHLH), TgbHLH87 was identified to positively regulate the <i>TgMLS</i> expression via directly binding the <i>TgMLS</i> promoter. Our finding contributes to mechanism underlying malate accumulation in <i>T. grandis</i> kernels.