The effect of mating system on growth of Arabidopsis lyrata in response to inoculation with the biotrophic parasite Albugo candida

The effects of variation in host reproductive systems on response to pathogens are not well understood. We inoculated individuals from outcrossing and inbreeding populations of North American Arabidopsis lyrata with Albugo candida (white blister rust) to test the effect of mating system and heterozygosity on disease response. We observed three host infection phenotypes, classified as fully resistant, partially resistant and fully susceptible. Overall, inbreeding populations had more susceptible and fewer partially resistant individuals than outcrossing populations, but the highest proportion of resistant individuals was found in two of the inbreeding populations. Mating system did not affect relative growth rate of inoculated plants, but there were strong effects of population and infection phenotype. We conclude that mating system per se does not determine the resistance of natural A. lyrata populations to infection by Albugo, but that the increased variability in responses among inbreeding populations may be due to reduced effective population size.     

Subcellular localization of cadmium in roots and leaves of Arabidopsis thaliana

We examined the subcellular cadmium (Cd) localization in roots and leaves of wild-type Arabidopsis thaliana (ecotype Columbia) exposed to environmentally relevant Cd concentrations. Energy-dispersive X-ray microanalysis (EDXMA) was performed on high-pressure frozen and freeze-substituted tissues. In the root cortex, Cd was associated with phosphorus (Cd/P) in the apoplast and sulfur (Cd/S) in the symplast, suggesting phosphate and phytochelatin sequestration, respectively. In the endodermis, sequestration of Cd/S was present as fine granular deposits in the vacuole and as large granular deposits in the cytoplasm. In the central cylinder, symplastic accumulation followed a distinct pattern illustrating the importance of passage cells for the uptake of Cd. In the apoplast, a shift of Cd/S granular deposits from the middle lamella towards the plasmalemma was observed. Large amounts of precipitated Cd in the phloem suggest retranslocation from the shoot. In leaves, Cd was detected in tracheids but not in the mesophyll tissue. Extensive symplastic and apoplastic sequestration in the root parenchyma combined with retranslocation via the phloem confirms the excluder strategy of Arabidopsis thaliana.     

Changes in carbohydrate metabolism and assimilate export in starch-excess mutants of Arabidopsis

The aim of this work was to investigate the effects on carbohydrate metabolism of a reduction in the capacity to degrade leaf starch in Arabidopsis. The major roles of leaf starch are to provide carbon for sucrose synthesis, respiration and, in developing leaves, for biosynthesis and growth. Wild-type plants were compared with plants of a starch-excess mutant line (sex4) deficient in a chloroplastic isoform of endoamylase. This mutant has a reduced capacity for starch degradation, leading to an imbalance between starch synthesis and degradation and the gradual accretion of starch as the leaves age. During the night the conversion of starch into sucrose in the mutant is impaired; the leaves of the mutant contained less sucrose than those of the wild type and there was less movement of ¹⁴C-label from starch to sucrose in radio-labelling experiments. Furthermore, the rate of assimilate export to the roots during the night was reduced in the mutant compared with the wild type. During the day however, photosynthetic partitioning was altered in the mutant, with less photosynthate partitioned into starch and more into sugars. Although the sucrose content of the leaves of the mutant was similar to the wild type during the day, the rate of export of sucrose to the roots was increased more than two-fold. The changes in carbohydrate metabolism in the mutant leaves during the day compensate partly for its reduced capacity to synthesize sucrose from starch during the night.     

Expression of the Arabidopsis thaliana invertase gene family

Two new loci have been found to be clustered with five other genes for the nitrate assimilation pathway in the Chlamydomonas reinhardtii genome. One gene, located close to the 3′-end of the high-affinity nitrate transporter (HANT) gene Nrt2;2, corresponds to the nitrite reductase (NiR) structural gene Nii1. This is supported by a number of experimental findings: (i) NiR-deficient mutants have lost Nii1 gene expression; (ii) Nii1 mRNA accumulation is co-regulated with the expression of other structural genes of the nitrate assimilation pathway; (iii) nitrite (nitrate) utilization ability is recovered in the NiR mutants by functional complementation with a wild-type Nii1 gene; (iv) the elucidated NII1 amino acid sequence is highly similar to that of the cyanobacterial and higher-plant enzyme, and contains the predicted domains for plastidic ferredoxin-NiRs. Thus, the mutant phenotype and the mRNA sequence and expression of the Nii1 gene have been unequivocally related. Accumulation of mRNA for the second locus identified, Lde1 (light-dependent expression), was not regulated by nitrogen, but like nitrate-assimilation clustered genes, its expression was down-regulated in the dark. Received: 27 November 1997 / Accepted: 19 January 1998     

Growth of Albugo candida (race unidentified) on Brassica juncea callus cultures

An obligate fungus Albugo candida (Pers. ex Lév.) Ktze. (race unidentified) was successfully grown on host callus tissues of Brassica juncea cv. Varuna. Of the various type of diseased explants used, young (green) hypertrophied inflorescence axis bearing non-erumpent zoosporangial blisters allowed the fungus to multiply asexually over the host calli on modified MS-medium (Murashige and Skoog, 1962). The dual cultures were maintained up to 6–8 subcultures without loss of viability of zoosporangia on MS-medium supplemented with 10.0 mg L^–1 IBA, 0.05 mg L^–1 kinetin, 25.0 mg L^–1 AA, 1.0 mg L^–1 biotin, 1.0 mg L^–1 thiamine-HCl and 1.0 g L^–1 casein hydrolysate. The fungus grew only on the callus cells and not axenically on the medium. Pathogenicity test and histopathology of cultures proved the existence of the viable fungus in vitro.Abbreviations AA ascorbic acid - BAP 6-benzyl aminopurine - CH casein hydrolysate acid hydrolysed - 2,4-D-2,4 dichlorophenoxy acetic acid - FAA formaldehyde acetic acid - IAA indole-3-acetic acid - IBA indole-3-butyric acid - HgCl₂ mercuric chloride - Kinetin 6-furfuryl aminopurine - MS Murashige and Skoog (1962) - NAA alpha naphthalene acetic acid - rh relative humidity - sdw sterile distilled water - wt. weights     

The efficiency of Arabidopsis thaliana (Brassicaceae) root hairs in phosphorus acquisition

Arabidopsis thaliana root hairs grow longer and denser in response to low-phosphorus availability. In addition, plants with the root hair response acquire more phosphorus than mutants that have root hairs that do not respond to phosphorus limiting conditions. The purpose of this experiment was to determine the efficiency of root hairs in phosphorus acquisition at high- and low-phosphorus availability. Root hair growth, root growth, root respiration, plant phosphorus uptake, and plant phosphorus content of 3-wk-old wild-type Arabidopsis (WS) were compared to two root hair mutants (rhd6 and rhd2) under high (54 mmol/m) and low (0.4 mmol/m) phosphorus availability. A cost-benefit analysis was constructed from the measurements to determine root hair efficiency. Under high-phosphorus availability, root hairs did not have an effect on any of the parameters measured. Under low-phosphorus availability, wild-type Arabidopsis had greater total root surface area, shoot biomass, phosphorus per root length, and specific phosphorus uptake. The cost-benefit analysis shows that under low phosphorus, wild-type roots acquire more phosphorus for every unit of carbon respired or unit of phosphorus invested into the roots than the mutants. We conclude that the response of root hairs to low-phosphorus availability is an efficient strategy for phosphorus acquisition.     

蛋白组学解析拟南芥响应细菌信号分子N-3-oxo-hexanoyl-homoserine-lactone（OHHL）的机制

细菌来源的群体感应信号分子能诱导与调控植物的抗病性与生长发育,本文用细菌群体感应信号分子N一3-oxo—hexanoyl-homoserine—lactone（OHHL）对拟南芥进行不同时间的处理,提取蛋白进行双向电泳分析,用蛋白组学的方法解析拟南芥响应细菌信号分子的机制。双向电泳与质谱分析共鉴定出47个点,这些蛋白中随处理时间的增加表达量上调的蛋白点数目增加,并且与植物抗氧化、物质代谢和细胞信号转导密切相关。因此通过蛋白组学分析结果可以更好的解释植物与细菌的相互作用机制,进一步利用其之间的联系来促进植物更好的生长发育。     

Analysis of two linked genes coding for the acyl carrier protein (ACP) from Arabidopsis thaliana (columbia)

Two linked genes, A1 and A2, coding for nearly identical isoforms of the acyl carrier protein (ACP) were isolated from an Arabidopsis thaliana (columbia) genomic library and sequenced. The amino acids deduced from the nucleotide sequence of the two genes indicate they encode distinct transit peptides, but the mature proteins are the same except for residue 79. Both genes are predicted to contain three introns in similar positions, although they differ in sequence and length. The introns interrupt regions coding for a) the transit peptide, b) the junction of the transit peptide and mature protein, and c) the highly conserved domain surrounding serine 38 to which the phosphopantetheine is attached. Primer extension analysis indicates that at least A1 is active in young plants.     

The size and sequence organization of the centromeric region of Arabidopsis thaliana chromosome 4.

We have determined the genome structure of the centromeric region of Arabidopsis thaliana chromosome 4 by sequence analysis of BAC clones obtained by genome walking, followed by construction of a physical map using DNA of a hypomethylated strain. The total size of the centromeric region, corresponding to the recombinant inbred (RI) markers between mi87 and mi167, was approximately 5.3 megabases (Mb). This value is over 3 Mb longer than that previously estimated by the Arabidopsis Genome Initiative (Nature, 408, 796-815, 2000). Although we could not cover the entire centromeric region by BAC clones because of the presence of highly repetitive sequences in the middle (2.7 Mb), the cloned regions spanning approximately 1 Mb at both sides of the gap were newly sequenced. These results together with the reported sequences in the adjacent regions suggest that the centromeric region is principally composed of a central domain of 2.7 Mb, consisting of mainly 180-bp repeats and Athila elements, and upper and lower flanking regions of 1.55 Mb and 1 Mb, respectively. The flanking regions were predominantly composed of various types of transposable elements, except for the upper end moiety in which a large 5S rDNA array (0.65 Mb) and central domain-like sequence are present. Such an organization is essentially identical to the centromeric region of chromosome 5 reported previously.     

Effect of water restriction on carbohydrate metabolism and photosynthesis in mature maize leaves

The time course of the modifications induced by a mild water stress has been examined for photosynthesis and several traits of carbohydrate metabolism in adult leaves of two inbred maize lines of North American and European origins, respectively. An early response was a sharp increase of the acid soluble invertase activity in adult leaves, 3–4 d after initiation of water shortage. Accordingly, correlated accumulations of fructose, glucose and to a lesser extent sucrose were observed. In the most responsive genotype, invertase activity finally reached a value > 3 times larger than the control value. By contrast, sucrose phosphate synthase activity, measured either under saturating or limiting substrate conditions, was progressively reduced by 20–40% on the 5th day and by 50–80% on the 7th day, depending on the genotype. Leaf photosynthetic rate was affected at approximately the same time as carbohydrate metabolism and stomatal conductance. Leaf water status, as measured by relative water content, declined afterwards. For all the observed responses, the two genotypes behaved very differently.     

拟南芥雄性不育突变体ms1502的遗传及定位分析

通过EMS诱变、背景纯化与遗传分析,从拟南芥（Arabidopsis thaliana）中筛选到了一棵隐性单基因控制的雄性不育突变体ms1502。细胞学观察发现,突变体在小孢子从四分体释放出后花药绒毡层过早衰亡,小孢子的内容物不正常地凝聚,最终无法形成正常的花粉粒。利用图位克隆的方法对该基因MSl502进行了定位,结果表明MS1502位于第4条染色体上分子标记F25124和T12H20之间105kb区间内。目前该区间内尚未见到花药发育必需基因（不育基因）的报道,因此MS1502是一个控制花粉发育的新基因。     

Gene conversion and the evolution of three leucine-rich repeat gene families in Arabidopsis thaliana

The high number of duplicated genes in plant genomes provides a potential template for gene conversion and unequal crossing-over. Within a gene family these two processes can render all members homogeneous or generate diversity by reassorting variants among paralogs. The latter is especially feasible in families where gene diversity confers a selective advantage and thus conversion events are likely to be retained. Consequently, the most complete record of gene conversion is expected to be most evident in gene families commonly subjected to positive selection. Here, we describe the extent and characteristics of gene conversion and unequal crossing-over in the coding and noncoding regions of nucleotide-binding site leucine-rich repeat (NBS-LRR), receptor-like kinases (RLK), and receptor-like proteins (RLP) in the plant Arabidopsis thaliana. Members of these three gene families are associated with disease resistance and their pathogen-recognition domain is a documented target of positive selection. Our bioinformatic approach to study the major family features that may influence gene conversion revealed that in these families there is a significant association between the occurrence of gene conversion and high levels of sequence similarity, close physical clustering, gene orientation, and recombination rate. We discuss these results in the context of the overlap between gene conversion and positive selection during the evolutionary expansion of the NBS-LRR, RLK, and RLP gene families.     

一个钙调蛋白类基因对拟南芥叶片气孔分布的影响

以一个缺磷胁迫诱导的钙调蛋白类基因AtPsiCaM为研究对象,采用拟南芥浸润转基因方法获得了AtPsiCaM基因的35S增强转基因植株。经Northern杂交检测表明,在AtPsiCaM基因的增强转基因株系中,该基因的转录水平明显增强。实验结果表明AtPsiCaM基因降低了增强转基因植株叶片的气孔指数和气孔导度,并且影响了植株的气孔分布。     

The soybean ENOD40(2) promoter is active in Arabidopsis thaliana and is temporally and spatially regulated

The ENOD40 gene is induced early during Rhizobium-legume symbiosis and has probably a primary role in the nodule organogenesis. In this paper we show that the 1.7 kb 5-flanking region of the GmENOD40(2) is able to drive the expression of a gusA-int marker in transgenic Arabidopsis thaliana. The promoter activity is developmentally regulated and the major activity is detected in the root and in the stigma.     

The effect of daylength on the transition to flowering in phytochrome-deficient, late-flowering and double mutants of Arabidopsis thaliana

The effect of daylength on flowering was investigated in the following mutants of Arabidopsis thaliana : phytochrome B deficient ( hy3=phyB ); phytochrome chromophore deficient ( hy2 ); late-flowering ( co, gi. fca and fwa ); the hy2 and hy3 , late-flowering double mutants and the hy2, hy3 , late-flowering triple mutants. The hy mutants flower with fewer rosette leaves than the Landsberg erecta wild type under both long day and short day conditions and express this effect to a different degree in all late-flowering mutant backgrounds and under both daylengths, with the exception of fca under short days. The number of cauline leaves and days to flowering is less affected by the hy genotype. The hy2, hy3 double mutants flower with even fewer rosette leaves than the hy2 and hy3 monogenic mutants, suggesting an inhibitory role for phytochrome B and other stable phytochromes on flowering. The complex interaction between phytochrome, daylength and the effect of the late-flowering genes on the various parameters that describe the transition to flowering in Arabidopsis is discussed.     

超声破碎拟南芥原生质体后的再生培养初报

拟南芥原生质体在超声破碎过滤后,对其叶绿体、细胞核等细胞器进行再生培养.观察到超声破碎对叶绿体有一定破坏作用导致叶绿体在蓝色荧光下不发荧光,在培养115 h后叶绿体有聚集现象;细胞核明显增多;出现内质网的明亮绿色荧光点.细胞核和内质网都是形成新原生质体的必要细胞器,通过对其再生培养可为细胞器重组乃至细胞重建提供启示.