Yuki Yoshida

SCREAM/ICE1 and SCREAM2 Specify Three Cell-State Transitional Steps Leading to Arabidopsis Stomatal Differentiation

Differentiation of specialized cell types in multicellular organisms requires orchestrated actions of cell fate determinants. Stomata, valves on the plant epidermis, are formed through a series of differentiation events mediated by three closely related basic-helix-loop-helix proteins: SPEECHLESS (SPCH), MUTE, and FAMA. However, it is not known what mechanism coordinates their actions. Here, we identify two paralogous proteins, SCREAM (SCRM) and SCRM2, which directly interact with and specify the sequential actions of SPCH, MUTE, and FAMA. The gain-of-function mutation in SCRM exhibited constitutive stomatal differentiation in the epidermis. Conversely, successive loss of SCRM and SCRM2 recapitulated the phenotypes of fama, mute, and spch, indicating that SCRM and SCRM2 together determined successive initiation, proliferation, and terminal differentiation of stomatal cell lineages. Our findings identify the core regulatory units of stomatal differentiation and suggest a model strikingly similar to cell-type differentiation in animals. Surprisingly, map-based cloning revealed that SCRM is INDUCER OF CBF EXPRESSION1, a master regulator of freezing tolerance, thus implicating a potential link between the transcriptional regulation of environmental adaptation and development in plants.

Jasmonic acid control of GLABRA3 links inducible defense and trichome patterning in Arabidopsis

Once attacked by herbivores, plants regenerate new leaves with increased trichome density as an inducible defense. Trichomes are specified from neighboring epidermal cells through local cell-cell interactions in the leaf primordia. However, the molecular mechanism of how herbivore-induced damage at older leaves remodels the pattern of trichome fate specification at newly forming leaves is largely unknown. In this study, we show that mutations in either the biosynthetic or signaling pathway of jasmonates (JAs), long-distance wound signals, abolish the wound-induced formation of trichomes. To identify the factors linking JA signaling to trichome fate specification, we isolated a novel class of mutants, unarmed (urm), which lack trichome induction but show otherwise normal responses to JAs. URM9 encodes an Importin β family protein, and URM23 is identical to TRANSPARENT TESTA GLABRA1 (TTG1), the product of which interacts with the bHLH transcription factor GLABRA3 (GL3). Loss of either URM9 or URM23 disrupts the subnuclear localization of GL3, thus implicating GL3 in trichome induction. The expression of GL3 was enhanced by JA treatment prior to trichome initiation. Genetic analysis of multiple trichome mutants shows that GL3, in concert with the R2R3-Myb transcription factor GLABRA1 (GL1), promotes trichome fate in response to JA in a dosage-dependent manner. These results indicate that GL3 is a key transcription factor of wound-induced trichome formation acting downstream of JA signaling in Arabidopsis.

Analysis and Compensation of Transmitter IQ Imbalances in OFDMA and SC-FDMA Systems

One limiting issue in implementing high-speed wireless systems is the impairment associated with analog processing due to component imperfections. In uplink transmission of multiuser systems, a major source of such impairment is in-phase/quadrature-phase imbalance (IQI) introduced at multiple transmitters. In this paper, we deal with orthogonal-frequency-division multiple access (OFDMA) and single-carrier frequency-division multiple access (SC-FDMA) which have received attention in recent years as physical layer protocol in WiMAX and 3GPP Long Term Evolution (LTE) and analyze the effect of the transmitter (Tx) IQIs on OFDMA and SC-FDMA receivers. To cope with the interuser interference problem due to Tx IQIs, we propose a widely linear receiver for OFDMA and SC-FDMA systems and also propose a novel subcarrier allocation scheme, which has high tolerance to such Tx IQ distortion.

Rhodium-Catalyzed Linear Codimerization and Cycloaddition of Ketenes with Alkynes

A novel rhodium-catalyzed linear codimerization of alkyl phenyl ketenes with internal alkynes to dienones and a novel synthesis of furans by an unusual cycloaddition of diaryl ketenes with internal alkynes have been developed. These reactions proceed smoothly with the same rhodium catalyst, RhCl(PPh3)3, and are highly dependent on the structure and reactivity of the starting ketenes.

Selective Trimerization of Ethylene to Isohexenes Catalyzed by a Ruthenium(0) Complex

The oligomerization of ethylene is of considerable scientific and industrial interest as a route to linear and branched alkenes. Linear alkenes, especially 1-hexene, are key intermediates in the production of plasticizers, detergents, and surfactants, as well as comonomers for the production of linear lowdensity polyethylene (LLDPE), whereas branched alkenes are of interest as high-octane additives to motor fuel. In the traditional transition metal complex-catalyzed oligomerization of ethylene, the formation of alkene mixtures (C4–C16 alkenes) [4] is unavoidable due to a mathematical distribution (Schulz–Flory or Poisson). Therefore, specific alkenes must be obtained by fractional distillation. The known ethylene trimerization catalysts are based mainly on chromium compounds with nitrogen, oxygen, and/or sulfur ligands, as well as mono(cyclopentadienyl)titanium(II) complexes. Sen and co-workers reported the first simple “ligandless” tantalum-based catalyst, and Mashima and co-workers recently reported a modified tantalum catalyst using 3,6-bis(trimethylsilyl)-1,4-cyclohexadiene (BTCD) or its methyl derivative (MBTCD). Aside from Mashima’s catalyst, all of the trimerization catalysts reported to date have required large amounts of aluminum compounds such as methylaluminoxane (MAO) or other alkylating organometallic reagents such as (CH3)2Zn as a conventional catalyst activator. In sharp contrast, there are few examples of the trimerization of ethylene to branched C6 alkenes, isohexenes, and only two catalyst systems for this procedure, [NiBr2(PPh3)2]/ CH3AlCl2 [12] and [Pd(acac)2]/BF3·OEt2 (acac = acetylacetonate), [13] have been reported to date. We have previously developed several codimerizations and cotrimerizations of different alkenes with high atom efficiency. Among these, the unusual head-to-head dimerization of styrenes and linear codimerization of styrenes with ethylene proceeded smoothly with a zero-valent ruthenium catalyst, [Ru(h-cot)(h-dmfm)2] [15] (cot = 1,3,5-cyclooctatriene, dmfm = dimethyl fumarate), in the presence of primary alcohols to give (E)-1,4-diaryl-1-butenes and (E)-1-aryl-1-butenes, respectively, without aluminum compounds or alkylating organometallic reagents. We believe that these reactions proceed via ruthenacyclopentane intermediates derived from the oxidative cyclization of styrenes and/or styrenes with ethylene on an active ruthenium center. This result prompted us to develop a novel catalyst system for the selective trimerization of ethylene without the use of aluminum compounds or alkylating organometallic reagents. Firstly, the [Ru(h-cot)(h-dmfm)2]-catalyzed trimerization of ethylene (4.05 MPa) was examined in mesitylene at 110 8C for 24 h in the presence of 1-octanol to specifically give C6 alkenes (selectivity = 95 %, TON= 56), together with a small amount of butenes (selectivity = 5 %; Scheme 1). No alkenes larger than C8 were obtained at all.

Pre- and Post-Equalization and Frequency Diversity Combining Methods for Block Transmission with Cyclic Prefix

SUMMARY This paper proposes low-complexity pre- and postfrequency domain equalization and frequency diversity combining methods for block transmission schemes with cyclic prefix. In the proposed methods, the equalization and diversity combining are performed simultaneously in discrete frequency domain. The weights for the proposed equalizer and combiner are derived based on zero-forcing and minimummean-square error criteria. We demonstrate the performance of the proposed methods, including bit-error rate performance and peak-to-average power ratios of the transmitted signal, via computer simulations.

On the effect of transmitter IQ imbalance at OFDMA receivers

One limiting issue in implementing high-speed wireless systems is the impairment associated with analog processing due to component imperfections. In uplink transmission of multiuser systems, a major source of such impairment is IQ imbalance (IQI) introduced at multiple transmitters. In this paper, we analyze the effect of the transmitter (Tx) IQI on OFDMA receiver. To cope with the inter-user interference problem due to Tx IQI, we propose a novel subcarrier allocation scheme, which has high tolerance to such Tx IQ distortion.