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author:("Tang, jianji")
1.  hSSB1 regulates both the stability and the transcriptional activity of p53 
Cell Research  2012;23(3):423-435.
The tumor suppressor p53 is essential for several cellular processes that are involved in the response to diverse genotoxic stress, including cell cycle arrest, DNA repair, apoptosis and senescence. Studies of the regulation of p53 have mostly focused on its stability and transactivation; however, new regulatory molecules for p53 have also been frequently identified. Here, we report that human ssDNA binding protein SSB1 (hSSB1), a novel DNA damage-associated protein, can interact with p53 and protect p53 from ubiquitin-mediated degradation. Furthermore, hSSB1 also associates with the acetyltransferase p300 and is required for efficient transcriptional activation of the p53 target gene p21 by affecting the acetylation of p53 at lysine382. Functionally, the hSSB1 knockdown-induced abrogation of the G2/M checkpoint is partially dependent on p53 or p300. Collectively, our results indicate that hSSB1 may regulate DNA damage checkpoints by positively modulating p53 and its downstream target p21.
PMCID: PMC3587703  PMID: 23184057
hSSB1; p53; stability; transcriptional activity; acetylation
2.  Human KIAA1018/FAN1 nuclease is a new mitotic substrate of APC/CCdh1 
Chinese Journal of Cancer  2012;31(9):440-448.
A recently identified protein, FAN1 (FANCD2-associated nuclease 1, previously known as KIAA1018), is a novel nuclease associated with monoubiquitinated FANCD2 that is required for cellular resistance against DNA interstrand crosslinking (ICL) agents. The mechanisms of FAN1 regulation have not yet been explored. Here, we provide evidence that FAN1 is degraded during mitotic exit, suggesting that FAN1 may be a mitotic substrate of the anaphase-promoting cyclosome complex (APC/C). Indeed, Cdh1, but not Cdc20, was capable of regulating the protein level of FAN1 through the KEN box and the D-box. Moreover, the up- and down-regulation of FAN1 affected the progression to mitotic exit. Collectively, these data suggest that FAN1 may be a new mitotic substrate of APC/CCdh1 that plays a key role during mitotic exit.
PMCID: PMC3777502  PMID: 22854063
KIAA1018/FAN1; APC/C; Cdh1; cell cycle
3.  Legumes Can Increase Cadmium Contamination in Neighboring Crops 
PLoS ONE  2012;7(8):e42944.
Legumes are widely used in many cropping systems because they share their nitrogen fixation products and phosphorus mobilization activities with their neighbors. In the current study, however, we showed that co-cultivation with legumes increased cadmium (Cd) contamination in the adjacent crops. Both field and mesocosm experiments indicated that legumes increased Cd levels in edible parts and shoots of four neighboring crops and five maize varieties tested, regardless of the Cd levels in the soil. This enhanced Cd accumulation in crops was attributed to root interactions that alter the rhizosphere environment. Co-cultivation with legumes reduced soil pH, which somewhat increased the exchangeable forms of Cd. Our results have demonstrated the inevitable increases in Cd levels of crops as a direct result of co-cultivation with legumes even under situations when these levels are below the permissible threshold. With this new revelation, we need to consider carefully the current cropping systems involving legumes and perhaps to re-design the current and future cropping systems in view of avoiding food contamination by Cd.
PMCID: PMC3419222  PMID: 22905189
4.  Plant mortality varies with arbuscular mycorrhizal fungal species identities in a self-thinning population 
Biology Letters  2010;7(3):472-474.
Because arbuscular mycorrhizal fungal (AMF) species differ in stimulating the growth of particular host plant species, AMF species may vary in their effects on plant intra-specific competition and the self-thinning process. We tested this hypothesis using a microcosm experiment with Medicago sativa L. as a model plant population and four AMF species. Our results showed that the AMF species Glomus diaphanum stimulated host plant growth more than the other three AMF species did when the plants were grown individually. Glomus diaphanum also induced the highest rate of mortality in the self-thinning plant populations. We also found a positive correlation between mortality and growth response to colonization. Our results demonstrate that AMF species can affect plant mortality and the self-thinning process by affecting plant growth differently.
PMCID: PMC3097865  PMID: 21147829
arbuscular mycorrhizal fungi; Medicago sativa L.; plant mortality; plant self-thinning
5.  Selectivity by host plants affects the distribution of arbuscular mycorrhizal fungi: evidence from ITS rDNA sequence metadata 
Arbuscular mycorrhizal fungi (AMF) can form obligate symbioses with the vast majority of land plants, and AMF distribution patterns have received increasing attention from researchers. At the local scale, the distribution of AMF is well documented. Studies at large scales, however, are limited because intensive sampling is difficult. Here, we used ITS rDNA sequence metadata obtained from public databases to study the distribution of AMF at continental and global scales. We also used these sequence metadata to investigate whether host plant is the main factor that affects the distribution of AMF at large scales.
We defined 305 ITS virtual taxa (ITS-VTs) among all sequences of the Glomeromycota by using a comprehensive maximum likelihood phylogenetic analysis. Each host taxonomic order averaged about 53% specific ITS-VTs, and approximately 60% of the ITS-VTs were host specific. Those ITS-VTs with wide host range showed wide geographic distribution. Most ITS-VTs occurred in only one type of host functional group. The distributions of most ITS-VTs were limited across ecosystem, across continent, across biogeographical realm, and across climatic zone. Non-metric multidimensional scaling analysis (NMDS) showed that AMF community composition differed among functional groups of hosts, and among ecosystem, continent, biogeographical realm, and climatic zone. The Mantel test showed that AMF community composition was significantly correlated with plant community composition among ecosystem, among continent, among biogeographical realm, and among climatic zone. The structural equation modeling (SEM) showed that the effects of ecosystem, continent, biogeographical realm, and climatic zone were mainly indirect on AMF distribution, but plant had strongly direct effects on AMF.
The distribution of AMF as indicated by ITS rDNA sequences showed a pattern of high endemism at large scales. This pattern indicates high specificity of AMF for host at different scales (plant taxonomic order and functional group) and high selectivity from host plants for AMF. The effects of ecosystemic, biogeographical, continental and climatic factors on AMF distribution might be mediated by host plants.
PMCID: PMC3395829  PMID: 22498355
6.  Arbuscular mycorrhizal fungi alter plant allometry and biomass–density relationships 
Annals of Botany  2010;107(3):407-413.
Background and Aims
Plant biomass–density relationships during self-thinning are determined mainly by allometry. Both allometry and biomass–density relationship have been shown to vary with abiotic conditions, but the effects of biotic interactions have not been investigated. Arbuscular mycorrhizal fungi (AMF) can promote plant growth and affect plant form. Here experiments were carried out to test whether AMF affect plant allometry and the self-thinning trajectory.
Two experiments were conducted on Medicago sativa L., a leguminous species known to be highly dependent on mycorrhiza. Two mycorrhizal levels were obtained by applying benomyl (low AMF) or not (high AMF). Experiment 1 investigated the effects of AMF on plant growth in the absence of competition. Experiment 2 was a factorial design with two mycorrhizal levels and two plant densities (6000 and 17 500 seeds m−2). Shoot biomass, root biomass and canopy radius were measured 30, 60, 90 and 120 d after sowing. The allometric relationships among these aspects of size were estimated by standardized major axis regression on log-transformed data.
Key Results
Shoot biomass in the absence of competition was lower under low AMF treatment. In self-thinning populations, the slope of the log (mean shoot biomass) vs. log density relationship was significantly steeper for the high AMF treatment (slope = –1·480) than for the low AMF treatment (–1·133). The canopy radius–biomass allometric exponents were not significantly affected by AMF level, but the root–shoot allometric exponent was higher in the low AMF treatment. With a high level of AMF, the biomass–density exponent can be predicted from the above-ground allometric model of self-thinning, while this was not the case when AMF were reduced by fungicide.
AMF affected the importance of below-ground relative to above-ground interactions and changed root vs. shoot allocation. This changed allometric allocation of biomass and altered the self-thinning trajectory.
PMCID: PMC3043928  PMID: 21169608
Arbuscular mycorrhizal fungi; biomass–density relationship; canopy radius–biomass allometry; root–shoot biomass allometry; Medicago sativa; self-thinning
7.  Positive Feedback between Mycorrhizal Fungi and Plants Influences Plant Invasion Success and Resistance to Invasion 
PLoS ONE  2010;5(8):e12380.
Negative or positive feedback between arbuscular mycorrhizal fungi (AMF) and host plants can contribute to plant species interactions, but how this feedback affects plant invasion or resistance to invasion is not well known. Here we tested how alterations in AMF community induced by an invasive plant species generate feedback to the invasive plant itself and affect subsequent interactions between the invasive species and its native neighbors. We first examined the effects of the invasive forb Solidago canadensis L. on AMF communities comprising five different AMF species. We then examined the effects of the altered AMF community on mutualisms formed with the native legume forb species Kummerowia striata (Thunb.) Schindl. and on the interaction between the invasive and native plants. The host preferences of the five AMF were also assessed to test whether the AMF form preferred mutualistic relations with the invasive and/or the native species. We found that S. canadensis altered AMF spore composition by increasing one AMF species (Glomus geosporum) while reducing Glomus mosseae, which is the dominant species in the field. The host preference test showed that S. canadensis had promoted the abundance of AMF species (G. geosporum) that most promoted its own growth. As a consequence, the altered AMF community enhanced the competitiveness of invasive S. canadensis at the expense of K. striata. Our results demonstrate that the invasive S. canadensis alters soil AMF community composition because of fungal-host preference. This change in the composition of the AMF community generates positive feedback to the invasive S. canadensis itself and decreases AM associations with native K. striata, thereby making the native K. striata less dominant.
PMCID: PMC2927435  PMID: 20808770

Results 1-7 (7)