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C 4 plants are believed to have evolved from C 3 plants through various C 3 -C 4 intermediate stages in which a photorespiration-dependent CO 2 concentration system known as C 2 photosynthesis operates. Genes involved in the C 4 cycle were thought to be recruited from orthologs present in C 3 species and developed cell-specific expression during C 4 evolution. To understand the process of establishing C 4 photosynthesis, we performed whole-genome sequencing and investigated expression and mesophyll-or bundle-sheath-cell-specific localization of phosphoenolpyruvate carboxylase (PEPC), NADP-malic enzyme (NADP-ME), pyruvate, orthophosphate dikinase (PPDK) in C 3 , C 3 -C 4 intermediate, C 4 -like, and C 4 Flaveria species. While genome sizes vary greatly, the number of predicted protein-coding genes was similar among C 3 , C 3 -C 4 intermediate, C 4 -like, and C 4 Flaveria species. Cell-specific localization of the PEPC, NADP-ME, and PPDK transcripts was insignificant or weak in C 3 -C 4 intermediate species, whereas these transcripts were expressed celltype specific in C 4 -like species. These results showed that elevation of gene expression and cell-specific control of pre-existing C 4 cycle genes in C 3 species was involved in C 4 evolution. Gene expression was gradually enhanced during C 4 evolution, whereas cell-specific control was gained independently of quantitative transcriptional activation during evolution from C 3 -C 4 intermediate to C 4 photosynthesis in genus Flaveria.

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In electronic-type ferroelectrics, where dipole moments produced by the variations of electron configurations are aligned, the polarization is expected to be rapidly controlled by electric fields. Such a feature can be used for high-speed electric-switching and memory devices. Electronic-type ferroelectrics include charge degrees of freedom, so that they are sometimes conductive, complicating dielectric measurements. This makes difficult the exploration of electronic-type ferroelectrics and the understanding of their ferroelectric nature. Here, we show unambiguous evidence for electronic ferroelectricity in the charge-order (CO) phase of a prototypical ET-based molecular compound, α-(ET)2I3 (ET:bis(ethylenedithio)tetrathiafulvalene), using a terahertz pulse as an external electric field. Terahertz-pump second-harmonic-generation(SHG)-probe and optical-reflectivity-probe spectroscopy reveal that the ferroelectric polarization originates from intermolecular charge transfers and is inclined 27° from the horizontal CO stripe. These features are qualitatively reproduced by the density-functional-theory calculation. After sub-picosecond polarization modulation by terahertz fields, prominent oscillations appear in the reflectivity but not in the SHG-probe results, suggesting that the CO is coupled with molecular displacements, while the ferroelectricity is electronic in nature. The results presented here demonstrate that terahertz-pump optical-probe spectroscopy is a powerful tool not only for rapidly controlling polarizations, but also for clarifying the mechanisms of ferroelectricity.

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