Abstract
Rings or arcs of fungus-regulated plant growth occurring on the floor of woodlands and grasslands are commonly called “fairy rings”. Fairy chemicals, 2-azahypoxanthine (AHX), imidazole-4-carboxamide (ICA), and 2-aza-8-oxohypoxanthine (AOH), are plant growth regulators involved in the phenomenon. The endogeny and biosynthetic pathways of AHX and AOH in plants have already been proven, however, those of ICA have remained unclear. We developed a high-sensitivity detection method for FCs including ICA and the endogenous ICA was detected in some plants for the first time. The quantitative analysis of the endogenous level of ICA in rice and Arabidopsis were performed using 13C-double labeled ICA. In addition, the incorporation experiment and enzyme assay using the labeled compound into rice and partially purified fraction of rice indicated that ICA is biosynthesized from 5-aminoimidazole-4-carboxamide (AICA), a metabolite on the purine metabolic pathway. The relationship between ICA and AHX was also discussed based on quantitative analysis and gene expression analysis.
Highlights
Investigated by using rice that belongs to the same family as turfgrass and showed very similar response to 1
fairy chemicals (FCs) are chemically synthesized from a common precursor, 5-aminoimidazole-4-carboxamide (AICA, 4) (Supplementary Materials Fig. S1)14–17. 4 and its ribonucleotide (AICAR, 5) are common members on the purine metabolic pathway in plants, animals, and microorganisms. 5 is known as an intermediate of purine bases such as hypoxanthine, xanthine, and uric acid
In terms of the biosynthesis of FCs, we previously reported that [4-13C]-3 was detected in rice treated with [5-13C]-4 and [4-13C]-1 was not detected in the rice[10]
Summary
Investigated by using rice that belongs to the same family as turfgrass and showed very similar response to 1. A few years after the discovery of 1 and 2, 2-aza-8-oxohypoxanthine (AOH, 3) was isolated as a metabolite of 1 from 1-treated rice. This compound elongated the seedlings of bentgrass and rice like 110. Our data showed the endogenous existence of 1 and 3 in plants and discovered a new route on the purine metabolism in which 1 and 3 are produced from 4 (Fig. 1)[10]. We established the exhaustive detection method of FCs (1–3) and their metabolites (6–9) using LC-MS/ MS and proved the universal existence of 2 in plants. The molecular mechanism and the biosynthetic pathway of 2 in rice were discussed based on the oligo DNA microarrays and the incorporation experiments
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