Tropomyosin induces the synthesis of magnesian calcite in sea urchin spines.

Calcium carbonate is present in many biominerals, including in the exoskeletons of crustaceans and shells of mollusks. High Mg-containing calcium carbonate was synthesized by high temperatures, high pressures or high molecular organic matter. For example, biogenic high Mg-containing calcite is synthesized under strictly controlled Mg concentration at ambient temperature and pressure. The spines of sea urchins consist of calcite, which contain a high percentage of magnesium. In this study, we investigated the factors that increase the magnesium content in calcite from the spines of the sea urchin, Heliocidaris crassispina. X-ray diffraction and inductively coupled plasma mass spectrometry analyses showed that sea urchin spines contain about 4.8% Mg. The organic matrix extracted from the H. crassispina spines induced the crystallization of amorphous phase and synthesis of magnesium-containing calcite, while amorphous was synthesized without SUE (sea urchin extract). In addition, aragonite was synthesized by SUE treated with protease-K. HC tropomyosin was specifically incorporated into Mg precipitates. Recombinant HC-tropomyosin induced calcite contained 0.1-2.5% Mg synthesis. Western blotting of sea urchin spine extracts confirmed that HC tropomyosin was present in the purple sea urchin spines at a protein weight ratio of 1.5%. These results show that HC tropomyosin is one factor that increases the magnesium concentration in the calcite of H. crassispina spines.

Comparison of herbicide specificity of CYP81A cytochrome P450s from rice and a multiple-herbicide resistant weed, Echinochloa phyllopogon.

BACKGROUND: CYP81A cytochrome P450s (CYP81As) play a key role in herbicide detoxification in Poaceae plants. Crop CYP81As confer natural tolerance to multiple herbicides, whereas CYP81As in weeds disrupt herbicide action. Identifying differences in CYP81A herbicide specificity between crops and weeds could provide valuable information for controlling weeds. In this study, we quantitatively compared herbicide specificity between CYP81A6 from rice (Oryza sativa) and CYP81A12 and CYP81A21 from a weed, Echinochloa phyllopogon, using transgenic Escherichia coli and Arabidopsis. RESULTS: All three CYP81As metabolized the five tested herbicides and formed similar metabolites, with the highest relative activities of 400 to 580% toward bentazone compared to their activity on bensulfuron-methyl (defined as 100%). However, they showed differing activity toward propyrisulfuron. The relative activities of Echinochloa phyllopogon CYP81A12 (12.2%) and CYP81A21 (34.4%) toward propyrisulfuron were lower than that of rice CYP81A6 (98.5%). Additionally, rice CYP81A6 produced O-demethylated propyrisulfuron and hydroxylated products, whereas Echinochloa phyllopogon CYP81As produced only hydroxylated products. Arabidopsis expressing CYP81A12 and CYP81A21 exhibited lower levels of resistance against propyrisulfuron compared to that in Arabidopsis expressing CYP81A6. Homology modeling and in silico docking revealed that bensulfuron-methyl docked well into the active centers of all three CYP81As, whereas propyrisulfuron docked into rice CYP81A6 but not into Echinochloa phyllopogon CYP81As. CONCLUSION: The differing herbicide specificity displayed by rice CYP81A6 and Echinochloa phyllopogon CYP81A12 and CYP81A21 will help design inhibitors (synergists) of weed CYP81As, as well as develop novel herbicide ingredients that are selectively metabolized by crop CYP81As, to overcome the problem of herbicide resistance. © 2022 Society of Chemical Industry.