植物缺铁应答bHLH转录因子研究进展

铁是植物生命活动必需的微量元素之一,土壤中有效铁含量较低,易导致植物缺铁。bHLH转录因子家族多个成员参与植物缺铁响应,发挥重要的调控作用。为深入了解植物对缺铁的反应机制,文中对植物缺铁胁迫应答的bHLH转录因子的结构、分类和功能及其调控机制、介导的缺铁胁迫信号通路进行综述,为应用bHLH转录因子培育缺铁耐受作物或富铁作物提供理论依据和设计策略。     

Epigenetic functions enriched in transcription factors binding to mouse recombination hotspots

The regulatory mechanism of recombination is a fundamental problem in genomics, with wide applications in genome-wide association studies, birth-defect diseases, molecular evolution, cancer research, etc. In mammalian genomes, recombination events cluster into short genomic regions called "recombination hotspots". Recently, a 13-mer motif enriched in hotspots is identified as a candidate cis-regulatory element of human recombination hotspots; moreover, a zinc finger protein, PRDM9, binds to this motif and is associated with variation of recombination phenotype in human and mouse genomes, thus is a trans-acting regulator of recombination hotspots. However, this pair of cis and trans-regulators covers only a fraction of hotspots, thus other regulators of recombination hotspots remain to be discovered. In this paper, we propose an approach to predicting additional trans-regulators from DNA-binding proteins by comparing their enrichment of binding sites in hotspots. Applying this approach on newly mapped mouse hotspots genome-wide, we confirmed that PRDM9 is a major trans-regulator of hotspots. In addition, a list of top candidate trans-regulators of mouse hotspots is reported. Using GO analysis we observed that the top genes are enriched with function of histone modification, highlighting the epigenetic regulatory mechanisms of recombination hotspots.     

植物盐胁迫应答转录因子的研究进展

盐胁迫会导致植物受到初级的渗透胁迫和离子毒害以及次级的氧化胁迫和营养胁迫,严重制约了农业生产.植物盐胁迫应答转录因子能够通过调节下游靶基因的表达减轻盐胁迫对植物造成的伤害.文中基于土壤盐渍化及其对植物的危害、转录因子在植物盐胁迫信号转导网络中的中枢调节作用,综述了盐胁迫应答转录因子参与的盐胁迫信号转导途径、通过形成同源...     

植物TCP转录因子的作用机理及其应用研究进展

TCP转录因子是一类植物特有蛋白,含有保守的TCP domain,其中由60个氨基酸组成的b HLH结构是结合DNA和蛋白互作所必需的。TCP转录因子由于其广泛参与调控植物的生长发育过程(如分枝、株高、叶型、花型等)而备受关注。最近有报道显示,TCP转录因子在植物逆境胁迫应答中(如低温和高盐)同样发挥重要作用。TCP蛋白参与多种信号转导途径(如油菜素内酯、茉莉酸、赤霉素、细胞分裂素等),可能是连接生长发育和介导胁迫响应的一个交叉点。本文从分子生物学角度,系统综述了植物TCP转录因子的作用机理及其在激素应答、发育调控及环境胁迫响应等过程中的功能,以期为基因工程方法改良作物生长模式和抗性提供参考。     

Increases in air temperature can promote wind-driven dispersal and spread of plants

Long-distance dispersal (LDD) of seeds and pollen shapes the spatial dynamics of plant genotypes, populations and communities. Quantifying LDD is thus important for predicting the future dynamics of plants exposed to environmental changes. However, environmental changes can also alter the behaviour of LDD vectors: for instance, increasing air temperature may enhance atmospheric instability, thereby altering the turbulent airflow that transports seed and pollen. Here, we investigate temperature effects on wind dispersal in a boreal forest using a 10-year time series of micrometeorological measurements and a Lagrangian stochastic model for particle transport. For a wide range of dispersal and life history types, we found positive relations between air temperature and LDD. This translates into a largely consistent positive effect of +3°C warming on predicted LDD frequencies and spread rates of plants. Relative increases in LDD frequency tend to be higher for heavy-seeded plants, whereas absolute increases in LDD and spread rates are higher for light-seeded plants for which wind is often an important dispersal vector. While these predicted increases are not sufficient to compensate forecasted range losses and environmental changes can alter plant spread in various ways, our results generally suggest that warming can promote wind-driven movements of plant genotypes and populations in boreal forests.     

Root physiological factors involved in cool-season grass response to high soil temperature

High soil temperature is a critical factor limiting growth of cool-season grasses. This study was designed to examine changes in water, nutritional, and hormonal status in response to high soil temperature for creeping bentgrass (Agrostis stoloniferavar. palustris) and to compare the sensitivity of those parameters to high soil temperatures. Plants of ‘Penncross’ were exposed to 35 °C soil temperature (heat stress) or 20 °C (control) in water baths while air temperature was maintained at 20 °C in growth chambers. Turfgrass quality, shoot growth rate, and root biomass decreased below the control levels at 15, 15, and 10 days of heat stress, respectively, while root mortality increased above the control level at 5 days of heat stress. Relative water content (RWC) of leaves decreased below the control level at 15 days of heat treatment. Root N content increased while P and K content did not change over time at 35 °C. Shoot N, P, and K content decreased below the control level at 15, 15, and 10 days of heat stress, respectively. Root abscisic acid (ABA) content decreased below the control level at 10 days while shoot ABA content increased above the control level at 5 days. The content of cytokinins (zeatin (Z) and zeatin riboside (ZR), dihydrogen zeatin riboside (DHZR), and isopentenyl adenosine (iPA)) decreased below their respective control levels as early as 5 days of heat stress for roots and 10 days for shoots. The decline in cytokinin content was also more dramatic than changes in other parameters. Our results suggested that cytokinin was most sensitive to high soil temperature among parameters examined, suggesting that changes in cytokinins could serve as an early stress indicator for plant responses to high soil temperature; however, decreased water, nutrient (N, P, and K), and cytokinin content, and increased ABA could all contribute to the decline in shoot and root growth for creeping bentgrass exposed to high soil temperatures.     

Streptomycin mimics the cool temperature response in rice plants

Exogenous application of streptomycin to etiolated seedlings of rice (Oryza sativa L.) during growth in darkness at moderate temperatures induced the same type of chlorosis as that elicited by cool temperatures. A comparison of sensitive (Indica) and tolerant (Japonica) cultivars indicated a close relationship between sensitivity to streptomycin and cool temperatures. Immunoblot (Rubisco LSU, SSU; CF1 complex of H⁺-ATPase; NADPH-protochlorophyllide oxidoreductase) and Northern blot analyses of plastid-encoded genes (16S rRNA; rbcL; rpoB; petB) in the streptomycin-treated sensitive cultivars revealed that the normal etioplast development was specifically inhibited by the antibiotic. Furthermore, the antibiotic did not affect the expression of mitochondrion-encoded genes (18S rRNA; atpA), which are also unaffected by cool temperatures. These result suggest that the effect of the antibiotic is quite similar to that of cool temperatures.     

Epigenetic inheritance in rice plants

BACKGROUND AND AIMS: Epigenetics is defined as mechanisms that regulate gene expression without base sequence alteration. One molecular basis is considered to be DNA cytosine methylation, which reversibly modifies DNA or chromatin structures. Although its correlation with epigenetic inheritance over generations has been circumstantially shown, evidence at the gene level has been limited. The present study aims to find genes whose methylation status directly correlates with inheritance of phenotypic changes. METHODS: DNA methylation in vivo was artificially reduced by treating rice (Oryza sativa ssp. japonica) seeds with 5-azadeoxycytidine, and the progeny were cultivated in the field for > 10 years. Genomic regions with changed methylation status were screened by the methylation-sensitive amplified polymorphysm (MSAP) method, and cytosine methylation was directly scanned by the bisulfite mapping method. Pathogen infection with Xanthomonas oryzae pv. oryzae, race PR2 was performed by the scissors-dip method on mature leaf blades. KEY RESULTS: The majority of seedlings were lethal, but some survived to maturity. One line designated as Line-2 showed a clear marker phenotype of dwarfism, which was stably inherited by the progeny over nine generations. MSAP screening identified six fragments, among which two were further characterized by DNA blot hybridization and direct methylation mapping. One clone encoding a retrotransposon gag-pol polyprotein showed a complete erasure of 5-methylcytosines in Line-2, but neither translocation nor expression of this region was detectable. The other clone encoded an Xa21-like protein, Xa21G. In wild-type plants, all cytosines were methylated within the promoter region, whereas in Line-2, corresponding methylation was completely erased throughout generations. Expression of Xa21G was not detectable in wild type but was constitutive in Line-2. When infected with X. oryzae pv. oryzae, against which Xa21 confers resistance in a gene-for-gene manner, the progeny of Line-2 were apparently resistant while the wild type was highly susceptible without Xa21G expression. CONCLUSIONS: These results indicated that demethylation was selective in Line-2, and that promoter demethylation abolished the constitutive silencing of Xa21G due to hypermethylation, resulting in acquisition of disease resistance. Both hypomethylation and resistant trait were stably inherited. This is a clear example of epigenetic inheritance, and supports the idea of Lamarckian inheritance which suggested acquired traits to be heritable.     

Temperature and leaf osmotic potential as factors in the acclimation of photosynthesis to high temperature in desert plants

Seasonal changes in the high temperature limit for photosynthesis of desert winter annuals growing under natural conditions in Death Valley, California were studied using an assay based upon chlorophyll fluorescence. All species of this group were 6 to 9°C more tolerant of high temperature at the end of the growing season (May) than at its beginning (February). Over this same time period, the mean daily maximum air temperatures increased by 12°C. Laboratory studies have demonstrated that increases in thermal tolerance could be induced by increasing growth temperature alone. For plants growing under field conditions there was also a good correlation between the thermal tolerance of leaves and the osmotic potential of leaf water, indicating that increases in the concentrations of some small molecules might also confer increased thermal tolerance. Isolated chloroplast thylakoids subjected to increasing concentrations of sorbitol could be demonstrated to have increased thermal tolerance.     

The photoreceptors in the high irradiance response of plants

Several studies show that the high irradiance response (HIR) of plants is probably due to two photoreceptors. One of the photoreceptors is phytochrome, and the other is an unidentified pigment provisionally named heliochrome. One of the functions of heliochrome is the synthesis of phytochrome, using far-red and blue radiations of high intensities, to replace the phytochrome destroyed by light. Another possible function could be an interaction of heliochrome with a substance produced by phytochrome. The data presented show that heliochrome is a pigment with different properties from phytochrome. It shows a far-red/green reversibility. Heliochrome has been shown to participate with phytochrome in such HIRs as leaf movement in Albizzia and flowering in a long-day plant. The first event initiated by phytochrome and by heliochrome could be the generation of a strong positive, electrostatic charge in the cell membrane.