Hydration structures at biomolecular surfaces are essential for understanding the mechanisms of the various biofunctions and stability of biomolecules. Here, we demonstrate the measurement of local hydration structures using an atomic force microscopy system equipped with a low-noise deflection sensor. We applied this method to the analysis of the muscovite mica/water interface and succeeded in visualizing a hydration structure that is site-specific on a crystal. Furthermore, at the biomolecule/buffer solution interface, we found surface hydration layers that are more packed than those at the muscovite mica/water interface.

Momilactones are bioactive diterpenoids that contribute to plant defense against pathogens and allelopathic interactions between plants. Both cultivated and wild grass species ofOryzaandEchinochloa crus-galli(barnyard grass) produce momilactones using a biosynthetic gene cluster (BGC) in their genomes. The bryophyteCalohypnum plumiforme(formerlyHypnum plumaeforme) also produces momilactones, and the bifunctional diterpene cyclase geneCpDTC1/HpDTC1,which is responsible for the production of the diterpene framework, has been characterized. To understand the molecular architecture of the momilactone biosynthetic genes in the moss genome and their evolutionary relationships with other momilactone-producing plants, we sequenced and annotated theC. plumiformegenome. The data revealed a 150-kb genomic region that contains two cytochrome P450 genes, theCpDTC1/HpDTC1gene and the “dehydrogenase momilactone A synthase” gene tandemly arranged and inductively transcribed following stress exposure. The predicted enzymatic functions in yeast and recombinant assay and the successful pathway reconstitution inNicotiana benthamianasuggest that it is a functional BGC responsible for momilactone production. Furthermore, in a survey of genomic sequences of a broad range of plant species, we found that momilactone BGC is limited to the two grasses (OryzaandEchinochloa) andC. plumiforme, with no synteny among these genomes. These results indicate that while the gene cluster inC. plumiformeis functionally similar to that in rice and barnyard grass, it is likely a product of convergent evolution. To the best of our knowledge, this report of a BGC for a specialized plant defense metabolite in bryophytes is unique.

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We developed a novel method to drive the cantilever oscillation for frequency modulation atomic force microscopy (FM-AFM) in liquid environments using electrostatic excitation. The cantilever with a gold backside coating was vibrated by applying an oscillating bias voltage between the cantilever backside and an optically transparent electrode used as a liquid cell window. The frequency spectrum of the oscillation shows a simple resonance curve without spurious peaks. The method does not require electrical conductivity of samples at all. In fact, both muscovite mica and potassium chloride surfaces in aqueous solutions were successfully imaged on an atomic scale. #