Seed dispersal determines a plant's reproductive success, range expansion, and population genetic structures. Camellia japonica, a common evergreen tree in Japan, has been the subject of recent genetic studies of population structure, but its mode of seed dispersal has been assumed, without detailed study, to be barochory. The morphological and physiological features of C. japonica seeds, which are large and nutritious, suggest zoochorous dispersal, however. We compared actual distances between mother trees and seedlings with distances attributable to gravity dispersion only, to test the zoochory hypothesis of C. japonica. The animals that transport the seeds for caching were identified experimentally. We also examined the extent to which seed dispersal is affected by the behavior of animal vectors. Seed dispersal by Apodemus speciosus was confirmed by taking photographs of animals that were consuming seeds experimentally deposited on the ground. Camellia seeds hoarded by the rodents under the litter or soil were protected from drying. On the basis of microsatellite analysis of maternal tissue from the seed coat, the mother trees of 28 seedlings were identified. Maternity analysis revealed the average seed-dispersal distance from mother trees was 5.8 m±6.0 SD, a distance greater than initial dispersal by gravity alone. These results indicate that C. japonica is a zoochorous species dispersed by A. speciosus. Fifty percent of the seed dispersal occurred from mature evergreen forests to dwarf bamboo thickets. This directional seed dispersal would contribute to range expansion of C. japonica. Home range sizes of A. speciosus were 0.85 ha at most and covered with different types of vegetation, from evergreen forests to grassland. This low specificity of their microhabitat use might enhance seed dispersal to different types of vegetation.

Nuclear import of proteins that contain classical nuclear localization signals (NLS) is initiated by importin␣, a protein that recognizes and binds to the NLS in the cytoplasm. In this paper, we have cloned a cDNA for a novel importin ␣ homologue from rice which is in addition to our previously isolated rice importin ␣1a and ␣2, and we have named it rice importin ␣1b. In vitro binding and nuclear import assays using recombinant importin ␣1b protein demonstrate that rice importin ␣1b functions as a component of the NLS-receptor in plant cells. Analysis of the transcript levels for all three rice importin ␣ genes revealed that the genes were not only differentially expressed but that they also responded to darkadaptation in green leaves. Furthermore, we also show that the COP1 protein bears a bipartite-type NLS and its nuclear import is mediated preferentially by the rice importin ␣1b. These data suggest that each of the different rice importin ␣ proteins carry distinct groups of nuclear proteins, such that multiple isoforms of importin ␣ contribute to the regulation of plant nuclear protein transport.The most characteristic feature of an eukaryotic cell is the presence of a nuclear envelope, which separates the cell into two major compartments, the nucleus and the cytoplasm. Communication between these two compartments takes place through the nuclear pore complex (NPC) 1 (for review, see Refs.1-3). The NPC allows molecules smaller than 40 -60 kDa to diffuse across, while larger proteins and RNA-protein complexes must be actively transported through the NPC in a signal-mediated and energy-dependent manner. Nuclear proteins involved in nuclear activities, such as DNA replication, transcriptional RNA synthesis, and RNA splicing, must enter into the nucleus. Conversely, RNA, such as mRNA synthesized in the nucleus, must be transported into the cytoplasm where it is translated to protein. In plants, nucleocytoplasmic transport has been implicated in functional regulation of a number of plant photomorphogenesis related protein factors (4). For example, constitutive photomorphogenic 1 (COP1), a repressor of photomorphogenesis, has been shown to shuttle between the nucleus and cytoplasm in response to a change of light environment. COP1 exists predominantly in the cytoplasm in the light while it accumulates in the nucleus in the dark, suggesting that nuclear protein transport is an underlying mechanism for the regulation of COP1 activity (5). Multiple pathways of nucleocytoplasmic transport have been identified, each likely to be involved in carrying a distinct group of proteins (for review, see Refs. 3 and 6). Among them, the best characterized is the import of proteins containing a classical nuclear localization signal (NLS) that consists of either a short stretch of 3-5 basic amino acids or two basic domains separated by a spacer, referred to as monopartite and bipartite NLS, respectively (7). Yeast mating factor (Mat␣-2) contains a NLS consisting of basic and hydrophobic amino acid residues and has also been shown to...

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We recently isolated two cDNAs encoding importin L L homologues (rice importin L L1 and L L2), the first such homologues identified in plants. To address the function of rice importin L L1 in the process of nuclear import of proteins, we carried out in vitro binding and nuclear import assays. Recombinant protein of rice importin L L1 assembled a complex (PTAC) with rice importin K K1 and NLS protein, and also bound to the nuclear envelope of tobacco BY-2 cells. Ran-GTP, but not Ran-GDP, interacted with rice importin L L1 and dissociated the heterodimer formed between rice importin K K1 and rice importin L L1. An in vitro nuclear import assay using digitonin-permeabilized HeLa cells revealed that rice importin L L1 can mediate nuclear envelope docking of NLS proteins and their subsequent translocation into the nucleus. These data strongly suggest that rice importin L L1 functions as a component of the NLS receptor in plant cells.z 1998 Federation of European Biochemical Societies.