Abstract
Background: Phosphorus is one of the essential elements for plant growth and development, but the content of plant available phosphorus (Pi) in many soil types is low. As a fast-growing timber species, Chinese fir is in great demand of Pi, and the lack of Pi in soil restricts the increase of productivity of Chinese fir plantation. Root morphology and the synthesis and secretion of organic acids play an important role in the uptake of phosphorus, but the molecular mechanisms of Chinese fir in response to Pi deficiency are largely unexplored. Results: In this study, seedlings of Yang 061 clone were grown under three Pi supply levels (0, 5 and 10 mg·L-1 P) and morphological attributes, organic acid content and enzyme activity were measured, the transcriptome data of Chinese fir root system were obtained and the expression levels of phosphorus responsive genes and organic acid synthesis related genes on citric acid and glyoxylate cycle pathway were determined. The results showed that there were 50,808 Unigenes annotated from the transcriptome of Chinese fir roots. Among differentially expressed genes, seven genes of phosphate transporter family and seventeen genes of purple acid phosphatase family were up-regulated by Pi deficiency, two proteins of SPX domain were up-regulated and one was down-regulated. The metabolic pathways of the citric acid and glyoxylate cycle pathway were mapped, and the expression characteristics of the related Unigenes under different phosphorus treatments were analyzed. The genes involved in malic acid and citric acid synthesis were up-regulated, and the activities of the related enzymes were significantly enhanced under long-term stress. The contents of citric acid and malic acid in the roots of Chinese fir increased after 30days of Pi deficiency. Conclusion: The Chinese fir roots showed increased expression of citrate and malate synthesis genes, increased content of organic acids and enhanced activities of related enzymes under Pi deficiency. The results provide a new insight for revealing the molecular mechanism of Pi deficiency and the pathway of organic acid synthesis in Chinese fir roots.
Carboxylate anion generation in aqueous solution from carbonate radiolysis, a potential route for abiotic organic acid synthesis on Earth and beyond
