Tip growth: signaling in the apical dome

Signaling molecules, such as ROP/RAC GTPases and their regulators, reactive oxygen species (ROS) and phospholipids, play pivotal roles in the control of tip growth in pollen tubes and root hairs. They are often localized to the apical growing region of these cells, where their functions are tightly interconnected with cytoskeletal rearrangement and polar vesicle trafficking, which participate in tip growth as well as affect the generation and maintenance of the apical growing region. Recent advances in our understanding of the interface between these cellular activities and signaling in tip growth will be discussed.     

Regulation of the anaphase-promoting complex-separase cascade by transforming growth factor-beta modulates mitotic progression in bone marrow stromal cells

Alteration of the tumor microenvironment by aberrant stromal cells influences many aspects of cell biology, including differentiation of stem cells and tumor metastasis. The role of transforming growth factor (TGF)-β signaling in stromal cells of the tissue microenvironment is critical to both pathways. We examined murine marrow stromal cells with deletion of Smad3 and found that they have an altered cell cycle profile, with a higher fraction of cells in G2/M phase. Deletion of Smad3 significantly abrogates TGF-β signaling and suppresses phosphorylation of CDC27–anaphase-promoting complex (APC) during mitosis, thereby resulting in elevated cyclin-dependent kinase (CDK)1 activity via increased levels of cyclin B. Enhanced CDK1 activity due to deregulation of APC leads in turn to hyperphosphorylation of separase, impeding chromatid separation. A residue Ser1126Ala mutation in separase specifically abolished separase hyperphosphorylation in Smad3-deficient cells. The present results unveil a new function for the TGF-β pathway in the regulation of APC to mediate chromatid separation during mitosis.     

Ecology of seed germination of eight non-pioneer tree species from a tropical seasonal rain forest in southwest China

We compared various aspects of the seed biology of eight non-pioneer tree species from a tropical seasonal rain forest in Xishuangbanna, SW China, that differ in time of dispersal, size and fresh seed moisture content (MC). Seeds were tested for germination under laboratory conditions after dehydration to different moisture levels and under 3.5, 10 and 30% solar irradiances in neutral-shade houses. For six species, germination was also compared in forest understory (3.5% light) and center of a forest gap (32.5% light). Under continuous dehydration over activated silica gel, 100% of seeds of four species had lost the ability to germinate after 48 h, and those of all species except Castanopsis hystrix (decreased from >90 to 30% germination) had lost the ability to germinate after 120 h. Four species did not differ in final germination percentages at the three irradiances (i.e. uniform germination). However, final germination percentages of Horsfieldia pandurifolia and Litsea pierrei var. szemaois were significantly lower in 30% than in 10 or 3.5% light, and seeds of Antiaris toxicaria and C. hystrix germinated to higher percentages in 30 and 10% than in 3.5% light. Mean time to germination (MTG) of the eight species (forest and shade house data combined) ranged from 5–5 days for Pometia tomentosa to 72–207days for L. pierrei; MTG for four species was ≤21 days. There was no obvious relationship between relative desiccation resistance and either time of dispersal, MTG or uniformity of germination at the three light levels, or between seed size and MC or MTG. However, the relationship between seed MC at maturity (25–60% fresh mass basis) and MC at 50% loss of seed viability (12.4–42.5%) was significant. Seven of the species fit Garwood’s (Ecol Monogr 53:159–181, 1983) rapid-rainy germination syndrome and one, L. pierrei, either her delayed-rainy or intermediate-dry germination syndrome. However, fresh, non-dehydrated seeds of all eight species germinated in ≤30 days at constant 30°C in light.     

人脐血CD34+细胞在NOD/SCID小鼠免疫重建及其抗HBV作用的初步探讨

目的：探讨NOD／SCID（nonobese diabetic／severe combined immunodeficient）小鼠移植人脐带血（human umbilical cord blood,HUCB）CD34＋细胞后免疫重建的特性。建立hu—NOD／SCID人鼠嵌合模型并观察其人源化免疫细胞在小鼠体内的生长分化特性、存活时间及其对HBV感染的清除作用。方法：1．NOD／SCID小鼠于C0603．5Gy照射后24h内尾静脉输注HUCBCD34＋细胞;2．以流式细胞技术鉴定小鼠外周血中CD45＋,CD3＋,CD19＋,CD56＋等人源化细胞的比例;3．NOD／SCID小鼠于移植后第4wk注射HBV感染者血清并以未移植的NOD／SCID小鼠作为对照,注射同等量的患者血清;4．于感染后1、7、10、15天采血,免疫荧光定量PCR方法分别检测其HBV—DNA含量。结果：1．HUCBCD34＋细胞移植后第2wk,在小鼠外周血中检测出的CD3＋CD8＋T细胞、CD3＋CD4＋T细胞、CD19＋B细胞、CD56＋NK细胞的比例分别为18．6％、16．1％、13．1％和27．8％。各细胞比例随小鼠周龄而变化。所有移植小鼠存活时间均达9wk;2．移植后小鼠感染HBV血清后,病毒仅在感染后第一天检出,随后消失;未移植CD34＋细胞的小鼠外周血HBV—DNA一直维持在103水平：结论：1．NOD／SCID小鼠经射线照射后移植HUCBCD34＋细胞,在不加任何刺激因子的情况下小鼠可以长时间存活并重建免疫;2．hu—NOD／SCID人鼠嵌合模型小鼠免疫成功重建后,对HBV感染有快速的清除作用。     

Molecular mapping of leaf rust resistance gene <Emphasis Type="Italic">LrZH84</Emphasis> in Chinese wheat line Zhou 8425B

Leaf rust, caused by Puccinia triticina, is one of the most widespread diseases in common wheat (Triticum aestivum L.) worldwide. With the objective of identifying and mapping new genes for resistance to leaf rust, F₁, F₂ plants and F₃ lines from a cross between resistant line Zhou 8425B and susceptible line Chinese Spring were inoculated with Chinese P. triticina races THTT and MBHP in the greenhouse. A total of 793 pairs of SSR primers were used to test the parents and resistant and susceptible bulks. Seven polymorphic chromosome 1B markers were used for genotyping the F₂ and F₃ populations. Zhou 8425B carried a single dominant resistance gene, temporarily designated LrZH84, linked to SSR markers gwm582 and barc8 with genetic distances of 3.9 and 5.2 cM, respectively. The Xbarc8 allele co-segregated with Lr26 in the F₃ population. The Xgwm582 allele associated with LrZH84 was identified as a leaf rust resistance gene and shown to be present in the Predgornaia 2 parent of Zhou 8425B. The seedling reaction pattern of LrZH84 was different from those of lines with Lr26, Lr33, Lr44 and Lr46, all of which are located in chromosome 1B. It was concluded that LrZH84 is likely to be a new leaf rust resistance gene.     

The decoupling of Smoothened from Galphai proteins has little effect on Gli3 protein processing and Hedgehog-regulated chick neural tube patterning

The Hedgehog (Hh) signal is transmitted by two receptor molecules, Patched (Ptc) and Smoothened (Smo). Ptc suppresses Smo activity, while Hh binds Ptc and alleviates the suppression, which results in activation of Hh targets. Smo is a seven-transmembrane protein with a long carboxyl terminal tail. Vertebrate Smo has been previously shown to be coupled to Gα_i proteins, but the biological significance of the coupling in Hh signal transduction is not clear. Here we show that although inhibition of Gα_i protein activity appears to significantly reduce Hh pathway activity in Ptc^−/− mouse embryonic fibroblasts and the NIH3T3-based Shh-light cells, it fails to derepress Shh- or a Smo-agonist-induced inhibition of Gli3 protein processing, a known in vivo indicator of Hh signaling activity. The inhibition of Gα_i protein activity also cannot block the Sonic Hedgehog (Shh)-dependent specification of neural progenitor cells in the neural tube. Consistent with these results, overexpression of a constitutively active Gα_i protein, Gα_i2QL, cannot ectopically specify the neural cell types in the spinal cord, whereas an active Smo, SmoM2, can. Thus, our results indicate that the Smo-induced Gα_i activity plays an insignificant role in the regulation of Gli3 processing and Shh-regulated neural tube patterning.     

Differential responses of lipid peroxidation and antioxidants in <Emphasis Type="Italic">Alternanthera philoxeroides</Emphasis> and <Emphasis Type="Italic">Oryza sativa</Emphasis> subjected to drought stress

To evaluate oxidative stress and the plant antioxidant system of Alternanthera philoxeroides [Mart.] Griseb and Oryza sativa L. in the response to drought, root and leaf tissues of drought-treated A. philoxeroides and O. sativa were collected and relative water content, stomatal conductance, the concentrations of malondialdehyde, proline and the activities of superoxide dismutase, peroxidases, catalase and total antioxidative activity investigated. The results showed that drought treatment had almost no effect on relative water content in A. philoxeroides but reduced relative water content in O. sativa. A. philoxeroides maintained a greater stomatal conductance than O. sativa under drought stress. In A. philoxeroides levels of lipid peroxidation were lower than in O. sativa and did not change during the experiment. After exposure to drought, concentrations of proline and activities of superoxide dismutase, peroxidases and catalase in A. philoxeroides were between 10% and 30% higher than in O. sativa, whereas total antioxidative activity in A. philoxeroides was several-fold higher than in O. sativa.     

脆性组氨酸三联体与复制蛋白A相互作用关键氨基酸残基的鉴定

目的：研究脆性组氨酸三联体（Fhit）对ATR/CHK1通路的影响,在确定Fhit与复制蛋白A（RPA）存在相互作用的基础上鉴定Fhit与RPA相互作用的关键氨基酸残基,为进一步研究Fhit特异的信号通路奠定基础。方法：构建一系列Fhit缺失突变体基因Fhit1～Fhit11及6种Fhit点突变体基因,将这些基因插入含GST基因的原核表达载体中,在大肠杆菌中表达并纯化GST-Fhit1～GST-Fhit11融合蛋白、突变体GST-FhitSIYEEL、GST-FhitIY、GST-FhitEL、GST-FhitF、GST-FhitA,以及GST-FhitD融合蛋白,用GST沉降技术研究Fhit与RPA相互作用的关键氨基酸残基。结果：Fhit蛋白第112～117（SIYEEL）残基可能是Fhit与RPA相互作用的关键区域,而第114（Y）残基可能是Fhit与RPA相互作用的关键氨基酸残基。结论：确定了Fhit与RPA相互作用的关键氨基酸残基,为阐明Fhit在维持基因组完整性方面的机理提供了线索。