Leaf senescence, which constitutes the final stage of leaf development, involves programmed cell death and is intricately regulated by various internal and environmental signals that are incorporated with age-related information. ABA plays diverse and important physiological roles in plants, and is involved in various developmental events and stress responses. ABA has long been regarded as a positive regulator of leaf senescence. However, the cellular mediators of ABA-induced senescence have not been identified. We sought to understand the ABA-induced senescence signaling process in Arabidopsis by examining the function of an ABA- and age-induced gene, RPK1, which encodes a membrane-bound, leucine-rich repeat-containing receptor kinase (receptor protein kinase 1). Loss-of-function mutants in RPK1 were significantly delayed in age-dependent senescence. Furthermore, rpk1 mutants exhibited reduced sensitivity to ABA-induced senescence but little change to jasmonic acid- or ethylene-induced senescence. RPK1 thus mediates ABA-induced leaf senescence as well as age-induced leaf senescence. Conditional overexpression of RPK1 at the mature stage clearly accelerated senescence and cell death, whereas induction of RPK1 at an early developmental stage retarded growth without triggering senescence symptoms. Therefore, RPK1 plays different roles at different stages of development. Consistently, exogenously applied ABA affected leaf senescence in old leaves but not in young leaves. The results, together, showed that membrane-bound RPK1 functions in ABA-dependent leaf senescence. Furthermore, the effect of ABA and ABA-inducible RPK1 on leaf senescence is dependent on the age of the plant, which in part explains the mechanism of functional diversification of ABA action.

SummaryLeaf senescence is the final stage of leaf development and is finely regulated via a complex genetic regulatory network incorporating both developmental and environmental factors. In an effort to identify negative regulators of leaf senescence, we screened activation-tagged Arabidopsis lines for mutants that exhibit a delayed leaf senescence phenotype. One of the mutants (ore7-1D) showed a highly significant delay of leaf senescence in the heterozygous state, leading to at least a twofold increase in leaf longevity. The activated gene (ORE7/ESC) encoded a protein with an AT-hook DNA-binding motif; such proteins are known to co-regulate transcription of genes through modification of chromatin architecture. We showed that ORE7/ ESC, in addition to binding to a plant AT-rich DNA fragment, could also modify the chromatin architecture, as illustrated by an altered distribution of a histone-GFP fusion protein in the nucleus of the mutant. Globally altered gene expression, shown by microarray analysis, also indicated that activation of ORE7/ESC results in a younger condition in the mutant leaves. We propose that ectopically expressed ORE7/ESC is negatively regulating leaf senescence and suggest that the resulting chromatin alteration may have a role in controlling leaf longevity. Interestingly, activation of ORE7/ESC also led to a highly extended post-harvest storage life.

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SummaryIn rice, limited efforts have been made to identify genes by the use of insertional mutagens, especially heterologous transposons such as the maize Ac/Ds. We constructed Ac and gene trap Ds vectors and introduced them into the rice genome by Agrobacterium-mediated transformation. In this report, rice plants that contained single and simple insertions of T-DNA were analysed in order to evaluate the gene-tagging ef®ciency. The 3¢ end of Ds was examined for putative splicing donor sites. As observed in maize, three splice donor sites were identi®ed at the 3¢ end of the Ds in rice. Nearly 80% of Ds elements were excised from the original T-DNA sites, when Ac cDNA was expressed under a CaMV 35S promoter. Repetitive ratoon culturing was performed to induce new transpositions of Ds in new plants derived from cuttings. About 30% of the plants carried at least one Ds which underwent secondary transposition in the later cultures. Eight per cent of transposed Ds elements expressed GUS in various tissues of rice panicles. With cloned DNA adjacent to Ds, the genomic complexities of the insertion sites were examined by Southern hybridization. Half of the Ds insertion sites showed simple hybridization patterns which could be easily utilized to locate the Ds. Our data demonstrate that the Ac/Ds-mediated gene trap system could prove an excellent tool for the analysis of functions of genes in rice. We discuss genetic strategies that could be employed in a large scale mutagenesis using a heterologous Ac/Ds family in rice.

A solution for overcoming the low reactivity of terephthalic acid and isosorbide (ISB) is proposed that uses 1,4cyclohexane dimethanol and ethylene glycol. Using the different reactivities, volatilities, and degree of steric hindrances among the three diols, a highly heat-resistive biobased terpolyester (PEICT; glass transition temperature = 93−143 °C) was synthesized with a high degree of polymerization (weight-average molecular weight 65 400; number-average molecular weight 25 400). After esterification, most of the oligomer end groups were found to consist of ISB, which decreases the overall reactivity of transesterification due to its characteristics. However, this end group changed gradually into ethylene units, which accelerated the transesterification and chain growth in the polycondensation process via chain scission at the carbonyl carbon adjacent to the ethylene unit. To substantiate this mechanism, the Fukui function was used to calculate the reactivity difference between monomers. The sequence distribution was analyzed using 13 C-nuclear magnetic resonance to elucidate the function of each diol unit in transesterification. Finally, a polycondensation process for the PEICT terpolyester is proposed.

The demand for face masks is increasing exponentially due to the coronavirus pandemic and issues associated with airborne particulate matter (PM). However, both conventional electrostatic‐ and nanosieve‐based mask filters are single‐use and are not degradable or recyclable, which creates serious waste problems. In addition, the former loses function under humid conditions, while the latter operates with a significant air‐pressure drop and suffers from relatively fast pore blockage. Herein, a biodegradable, moisture‐resistant, highly breathable, and high‐performance fibrous mask filter is developed. Briefly, two biodegradable microfiber and nanofiber mats are integrated into a Janus membrane filter and then coated by cationically charged chitosan nanowhiskers. This filter is as efficient as the commercial N95 filter and removes 98.3% of 2.5 µm PM. The nanofiber physically sieves fine PM and the microfiber provides a low pressure differential of 59 Pa, which is comfortable for human breathing. In contrast to the dramatic performance decline of the commercial N95 filter when exposed to moisture, this filter exhibits negligible performance loss and is therefore multi‐usable because the permanent dipoles of the chitosan adsorb ultrafine PM (e.g., nitrogen and sulfur oxides). Importantly, this filter completely decomposes within 4 weeks in composting soil.

The genome of tobacco mosaic virus (TMV) encodes replicase protein(s), movement protein (MP), and capsid protein (CP). On infection, one or more viral proteins direct the assembly of virus replication complexes (VRCs), in association with host-derived membranes. The impact of CP-mediated resistance on the structures of the replication complexes was examined in nontransgenic and transgenic BY-2 cell lines that produce wild-type CP, mutant CP T42W , and Ds-Red, which was targeted to endoplasmic reticulum by using immunofluorescence and 3D microscopy. We developed a model of VRCs that shows a clear association of MP with and surrounding the endoplasmic reticulum. Replicase is located within the MP bodies, as well as isolated sites throughout the cell. CP surrounds the VRCs. CP enhances the production of MP and increases the size of the VRC; however, the mutant CP T42W reduces the amount of MP and interferes with the formation of VRCs. We propose a regulatory role of the CP in the establishment of the VRC. We suggest that the lack of formation of VRCs restricts the efficiency of virus replication and the formation of virus movement complexes, resulting in restriction of cell-cell spread of infection. This results in higher levels of plant CP-mediated protection provided by CP T42W . P ositive-strand RNA viruses share fundamental similarities in RNA replication despite differences in genome organization, virion morphology, and host range. On entering the cell, the messenger-sense genome is translated to yield a variety of proteins, some of which direct the assembly of virus replication complexes (VRCs) that are invariably associated with host membrane (1-4).The 6.3-kb (ϩ) sense RNA genome of tobacco mosaic virus (TMV) encodes two proteins essential for replication of the genome (replicase, 126͞183 kDa), a 30-kDa movement protein (MP) that is essential for cell-cell spread of infection, and a 17.5-kDa capsid protein (CP). Cytological studies of TMVinfected cells showed VRCs associated with cytoplasmatic inclusions bodies, called viroplasm [also called X-bodies (5)], that enlarge throughout infection. Electron microscopy revealed that these inclusion bodies contained ribosomes, tubules, and 126͞ 183-kDa replication proteins (6-9).Recent studies show that the 126-kDa protein associates with the endoplasmic reticulum (ER) in the absence of other viral proteins, and it was suggested that association may occur via either membrane-bound host proteins or a membrane insertion of an amphipathic helix detected in the protein (10). The MP behaves as an intrinsic membrane protein, promotes the formation of ER aggregates, and probably facilitates the establishment of TMV replication complexes that contain viral RNA, replicase, and MP (11-15).Transgenic plants that produce TMV CP interfere with disassembly of TMV and thereby confer resistance to TMV infection (16). Mutant CP that is changed at amino acid 42 [Thr-42 3 Trp (T42W)] interferes with virus disassembly. In addition, it reduces production of MP on infection, thereby reduci...

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