Rings or arcs of fungus-stimulated plant growth occur worldwide; these are commonly referred to as "fairy rings". In 2010, we discovered 2-azahypoxanthine (AHX), a compound responsible for the fairy-ring phenomenon caused by fungus; AHX stimulated the growth of all the plants tested. Herein, we reveal the isolation and structure determination of a common metabolite of AHX in plants, 2-aza-8-oxohypoxanthine (AOH). AHX is chemically synthesized from 5-aminoimidazole-4-carboxamide (AICA), and AHX can be converted into AOH by xanthine oxidase. AICA is one of the members of the purine metabolic pathway in animals, plants, and microorganisms. However, further metabolism of AICA remains elusive. Based on these results and facts, we hypothesized that plants themselves produce AHX and AOH through a pathway similar to the chemical synthesis. Herein, we demonstrate the existence of endogenous AHX and AOH and a novel purine pathway to produce them in plants.

In the present study, to investigate the mechanisms regulating carotenoid accumulation in citrus, a culture system was set up in vitro with juice sacs of three citrus varieties, Satsuma mandarin (Citrus unshiu Marc.), Valencia orange (Citrus sinensis Osbeck), and Lisbon lemon (Citrus limon Burm.f.). The juice sacs of all the three varieties enlarged gradually with carotenoid accumulation. The changing patterns of carotenoid content and the expression of carotenoid metabolic genes in juice sacs in vitro were similar to those ripening on trees in the three varieties. Using this system, the changes in the carotenoid content and the expression of carotenoid metabolic genes in response to environmental stimuli were investigated. The results showed that carotenoid accumulation was induced by blue light treatment, but was not affected by red light treatment in the three varieties. Different regulation of CitPSY expression, which was up-regulated by blue light while unaffected by red light, led to different changes in carotenoid content in response to these two treatments in Satsuma mandarin and Valencia orange. In all three varieties, increases in carotenoid content were observed with sucrose and mannitol treatments. However, the accumulation of carotenoid in the two treatments was regulated by distinct mechanisms at the transcriptional level. With abscisic acid (ABA) treatment, the expression of the genes investigated in this study was up-regulated in Satsuma mandarin and Lisbon lemon, indicating that ABA induced its own biosynthesis at the transcriptional level. This feedback regulation of ABA led to decreases in carotenoid content. With gibberellin (GA) treatment, carotenoid content was significantly decreased in the three varieties. Changes in the expression of genes related to carotenoid metabolism varied among the three varieties in response to GA treatment. These results provided insights into improving carotenoid content and composition in citrus during fruit maturation.

β-Cryptoxanthin (β-cry), an antioxidant abundant in citrus fruits, plays an important role in the prevention and treatment of certain diseases, especially cancers. In the present study, to increase the content of β-cry in citrus flavedo, the effects of blue (470 nm) and red (660 nm) light-emitting diode (LED) lights on the accumulation of carotenoids and expression of genes related to carotenoid biosynthesis were investigated in the flavedo of Satsuma mandarin. The results showed that accumulation of β-cry was induced by red light, while it was not affected by blue light. The accumulation of β-cry under red light was attributed to simultaneous increases in the expression of CitPSY, CitPDS, CitZDS, CitLCYb1, CitLCYb2, CitHYb, and CitZEP. The results presented herein might provide new strategies to enhance the commercial and nutritional value of citrus fruits.

Rings or arcs of fungus-regulated plant growth occur often on the floor of woodlands, in agricultural areas, and in grasslands worldwide. These rings are commonly called "fairy rings". A plant-growth regulating compound was isolated from a fairy ring forming fungus, Lepista sordida , and its chemical structure was identified as imidazole-4-carboxamide (ICA) by spectroscopic analyses including single-crystal X-ray diffraction techniques. ICA inhibited the growth of turfgrass and rice seedling. On the other hand, in a greenhouse experiment, this compound increased rice grain yield by 26% compared with control.

To better understand the mechanism of plastid differentiation from chloroplast to chromoplast, we examined proteome and plastid changes over four distinct developmental stages of ‘Micro-Tom’ fruit. Additionally, to discover more about the relationship between fruit color and plastid differentiation, we also analyzed and compared ‘Micro-Tom’ results with those from two other varieties, ‘Black’ and ‘White Beauty’. We confirmed that proteins related to photosynthesis remain through the orange maturity stage of ‘Micro-Tom’, and also learned that thylakoids no longer exist at this stage. These results suggest that at a minimum there are changes in plastid morphology occurring before all related proteins change. We also compared ‘Micro-Tom’ fruits with ‘Black’ and ‘White Beauty’ using two-dimensional gel electrophoresis. We found a decrease of CHRC (plastid-lipid-associated protein) and HrBP1 (harpin binding protein-1) in the ‘Black’ and ‘White Beauty’ varieties. CHRC is involved in carotenoid accumulation and stabilization. HrBP1 in Arabidopsis has a sequence similar to proteins in the PAP/fibrillin family. These proteins have characteristics and functions similar to lipocalin, an example of which is the transport of hydrophobic molecules. We detected spots of TIL (temperature-induced lipocalin) in 2D-PAGE results, however the number of spots and their isoelectric points differed between ‘Micro-Tom’ and ‘Black’/‘White Beauty’. Lipocalin has various functions including those related to environmental stress response, apoptosis induction, membrane formation and fixation, regulation of immune response, cell growth, and metabolism adjustment. Lipocalin related proteins such as TIL and HrBP1 could be related to the accumulation of carotenoids, fruit color and the differentiation of chromoplast.