Persistent infection, wherein a pathogen is continually present in a host individual, is widespread in virus-host systems. However, little is known regarding how seasonal environments alter virus-host interaction during such metastability. We observed a lineage-to-lineage infection of the host plant Arabidopsis halleri with Turnip mosaic virus for 3 years without severe damage. Virus dynamics and virus-host interactions within hosts were highly season dependent. Virus accumulation in the newly formed leaves was temperature dependent and was suppressed during winter. Transcriptome analyses suggested that distinct defence mechanisms, i.e. salicylic acid (SA)-dependent resistance and RNA silencing, were predominant during spring and autumn, respectively. Transcriptomic difference between infected and uninfected plants other than defence genes appeared transiently only during autumn in upper leaves. However, the virus preserved in the lower leaves is transferred to the clonal offspring of the host plants during spring. In the linage-to-linage infection of the A. halleri-TuMV system, both host clonal reproduction and virus transmission into new clonal rosettes are secured during the winter-spring transition. How virus and host overwinter turned out to be critical for understanding a long-term virus-host interaction within hosts under temperate climates, and more generally, understanding seasonality provides new insight into ecology of plant viruses.

: DNA methylation has been considered a stable epigenetic mark but may respond to fluctuating environments. However, it is unclear how they behave in natural environments. Here, we analyzed seasonal patterns of genome-wide DNA methylation in a single clone from a natural population of the perennial Arabidopsis halleri. The genome-wide pattern of DNA methylation was primarily stable, and most of the repetitive regions were methylated across the year. Although the proportion was small, we detected seasonally methylated cytosines (SeMCs) in the genome. SeMCs in the CHH context were detected predominantly at repetitive sequences in intergenic regions. In contrast, gene-body CG methylation (gbM) itself was generally stable across seasons, but the levels of gbM were positively associated with seasonal stability of RNA expression of the genes. These results suggest the existence of two distinct aspects of DNA methylation in natural environments: sources of epigenetic variation and epigenetic marks for stable gene expression.

Scaevola taccada is characterized by dimorphic fruits, with one type having cork and pulp (C-morph) and the other type having only pulp (NC-morph). Although within-individual dimorphism has not been observed, both morphs can occur at the same sites. The cork floats on seawater, and the pulp is eaten by birds. Thus, the morphs may have different seed dispersal abilities, via sea currents and birds, respectively. This study aimed to determine the functional characteristics of the dimorphic fruits. First, the potential seed dispersal ability of sea currents and birds was compared between the two fruits morphs by conducting a floating test and by measuring the proportions of different parts of the fruits, respectively. Next, the frequencies of the two morphs across different substrates (beaches, rocks, and cliffs) in the southern islands around Japan were analyzed. Most C-morph fruits remained floating for more than 180 days in a seawater tank, whereas all NC-morph fruits sank after approximately 1 week. The NC-morph fruits had a more pulp volume and less indigestible material than the C-morph fruits. Although both types of plants were found on many islands and all substrates, the C-morph was dominant on beaches, whereas the NC-morph was most frequent on cliffs. The frequencies of the morphs on different substrates might be influenced by the differences in their seed dispersal abilities. The two morphs may differ in fitness on different substrates. These findings improve our understanding of plant adaptations for dispersal.

No abstract

Mukojima is an uninhabited island in the northern part of the Ogasawara archipelago. The island's, vegetation was drastically disturbed by feral goats Capra aegagrus hircus after 1945. The change in the avifauna resulting from this habitat disturbance has previously been described. Japanese Bush Warbler Cettia diphone and Bonin Honeyeater Apalopteron familiare became locally extinct. In recent years, the goats have been exterminated and the vegetation is now recovering. To clarify the current stituaion of the avifauna on Mukojima, we counted bird numbers along two routes from March to June, 2007. We also recorded the vegetation along the routes. Many Japanese White-eye Zosterops japonicus (an introduced species) were observed in the forest, and several Blue Rock Thrush Monticola solitarius were observed in open areas. These were the only two species observed throughout our study period; both were confirmed to be breeding. Other native land birds, Common Buzzard Buteo buteo, Brown-eared Bulbul Hypsipetes amaurotis, White's Trush Zoothera dauma, Japanese Bush Warbler Cettia diphone were less abundant, with only a few individuals of each species observed for short periods. In the future, such vistors to Mukojima may increase as the vegetation recovers. Japanese White-eye will contribute to the recovery of the vegetation as they are both seed dispersers and pollinators, although they may compete with indigenous species for food.

Some introduced frugivorous birds disperse introduced plants and are thus a substitute for extinct native birds. Introduced birds have negative and/or infrequently positive effects on local ecosystems. It is important for management of the ecosystems to understand the relationships between native and introduced frugivorous and plant species. In this study, we elucidated these relationships in Mukojima Island, the Bonin Islands, where was anthropologically deforested and Japanese White-eye Zosterops japonicus and some plants were already introduced. We examined the habitat selection of frugivorous birds, actual dispersed seeds in bird feces, and the distribution of the potentially dispersed plant species. The Japanese White-eye and the native, Blue Rockthrush Monticola solitarius, were dominant on this island. The former mainly used the forest area and dispersed only small seeds and frequently introduced plant seeds. The latter mainly used the open area and dispersed both small and large seeds. Some small-seed plants occurred not only in the forest but also in the open area. Their seedlings were distributed farther from their adult trees than the large-seed species. These indicate that small-seed plants would be more spread than the large-seed plants because the two bird species disperse their seeds in different environments. This introduced bird species may be important in vegetation recovery, although it may contribute to the distribution of introduced plants on this island.

No abstract

20Organisms survive in naturally fluctuating environments by responding to 21 long-term signals, such as seasonality, by filtering out short-term noise. DNA 22 methylation (gbM) itself was generally stable across seasons, but the levels of 36 gbM were positively associated with seasonal stability of RNA expression of the 37 genes. These results suggest the existence of two distinct aspects of DNA 38 methylation in natural environments: sources of epigenetic variation and 39 epigenetic marks for stable gene expression. 40Keywords: Arabidopsis halleri, DNA methylation, Natural environment, 41 seasonal changes, seasonally methylated cytosines 42 6 manner (15, 16). Therefore, it is difficult to predict whether DNA methylation is 59 stable or dynamic under natural conditions. Recently the need for 'in natura' 60 studies has been highlighted in order to understand how organisms respond to 61 environmental signals by filtering out innumerable fluctuations and noise (17, 18). 62In the temperate regions, seasonality is the most prominent cause of 63 environment fluctuations. However, we still do not understand how DNA 64 methylation behaves across seasons. 65In order to reveal the seasonal dynamics of DNA methylation, here, we 66 conducted an "in natura" study on genome-wide DNA methylation using a single 67 clone growing in a population of Arabidopsis halleri (L.) O'Kane & Al-Shehbaz 68 subsp. gemmifera (Matsum.) O'Kane & Al-Shehbaz (hereafter referred to as A. 69 haleri), a close relative of Arabidopsis thaliana. Its clonal propagation and 70 perennial life-cycle allowed us to sample leaves all year round from the single 71 clonal individual (19). We studied seasonal dynamics of key flowering-time 72genes and whole transcriptome previously in the site (20, 21). In this study, to 73 understand the dynamics of DNA methylation, we performed whole-genome 74