The shooty callus induced by suppression of tobacco CHRK1 receptor-like kinase is a phenocopy of the tobacco genetic tumor

CHRK1 encodes a tobacco receptor-like kinase that contains a chitinase-like sequence in the extracellular domain. In a previous study, CHRK1-suppressed transgenic tobacco plants exhibited pleiotropic developmental abnormalities including spontaneous growth of shooty callus from emerging embryos in the absence of any exogenous hormones. In this study, we show that the CHRK1 shooty callus mimics tobacco genetic tumors in its morphology, physiology, and gene expression profiles. Similar to CHRK1 shooty callus, tobacco genetic tumors exhibit shooty callus morphology and hormone-independent shoot organogenesis. Both the CHRK1 callus and genetic tumors constitutively expressed KNOTTED1-type homeobox genes at the high levels, consistent with their vigorous shoot formation. These two types of calli exhibited cell death phenotypes, accompanied by high H₂O₂ production, increased ion leakage, and callose accumulation. Consistently, both types of calli constitutively expressed high levels of defense genes induced during pathogen-mediated HR cell death. These results, together with previous reports that both the CHRK1 shooty callus and tobacco genetic tumor contained high levels of cytokinin, indicate that CHRK1 shooty callus is a phenocopy of tobacco genetic tumor. CHRK1-mediated signal transduction may play a role in the formation of the genetic tumor in tobacco.     

Many amino acid substitution variants identified in DNA repair genes during human population screenings are predicted to impact protein function

Over 520 different amino acid substitution variants have been previously identified in the systematic screening of 91 human DNA repair genes for sequence variation. Two algorithms were employed to predict the impact of these amino acid substitutions on protein activity. Sorting Intolerant from Tolerant (SIFT) classified 226 of 508 variants (44%) as "Intolerant." Polymorphism Phenotyping (PolyPhen) classed 165 of 489 amino acid substitutions (34%) as "Probably or possibly damaging." Another 9-15% of the variants were classed as "Potentially intolerant or damaging." The results from the two algorithms are highly associated, with concordance in predicted impact observed for approximately 62% of the variants. Twenty-one to thirty-one percent of the variant proteins are predicted to exhibit reduced activity by both algorithms. These variants occur at slightly lower individual allele frequency than do the variants classified as "Tolerant" or "Benign." Both algorithms correctly predicted the impact of 26 functionally characterized amino acid substitutions in the APE1 protein on biochemical activity, with one exception. It is concluded that a substantial fraction of the missense variants observed in the general human population are functionally relevant. These variants are expected to be the molecular genetic and biochemical basis for the associations of reduced DNA repair capacity phenotypes with elevated cancer risk.     

Two TIR:NB:LRR genes are required to specify resistance to Peronospora parasitica isolate Cala2 in Arabidopsis

Resistance responses that plants deploy in defence against pathogens are often triggered following a recognition event mediated by resistance (R) genes. The encoded R proteins usually contain a nucleotide-binding site (NB) and a leucine-rich repeat (LRR) domain. They are further classified into those that contain an N-terminal coiled coil (CC) motif or a Toll interleukin receptor (TIR) domain. Such R genes, when transferred into a susceptible plant of the same or closely related species, usually impart full resistance capability. We have used map-based cloning and mutation analysis to study the recognition of Peronospora parasitica (RPP)2 (At) locus in Arabidopsis accession Columbia (Col-0), which is a determinant of specific recognition of P. parasitica (At) isolate Cala2. Genetic mapping located RPP2 to a 200-kb interval on chromosome 4, which contained four adjacent TIR:NB:LRR genes. Mutational analysis revealed three classes of genes involved in specifying resistance to Cala2. One class, which resulted in pleiotropic effects on resistance to other P. parasitica (At) isolates, was unlinked to the RPP2 locus; this class included AtSGT1b. The other two classes were mapped within the interval and were specific to Cala2 resistance. Representatives of each of these classes were sequenced, and mutations were found in one or the other of two (RPP2A and RPP2B) of the four TIR:NB:LRR genes. RPP2A and RPP2B complemented their specific mutations, but failed to impart resistance when present alone, and it is concluded that both genes are essential determinants for isolate-specific recognition of Cala2. RPP2A has an unusual structure with a short LRR domain at the C-terminus, preceded by two potential but incomplete TIR:NB domains. In addition, the RPP2A LRR domain lacks conserved motifs found in all but three other TIR:NB:LRR class proteins. In contrast, RPP2B has a complete TIR:NB:LRR structure. It is concluded that RPP2A and RPP2B cooperate to specify Cala2 resistance by providing recognition or signalling functions lacked by either partner protein.     

Hidden biodiversity of the extremophilic Cyanidiales red algae

The Cyanidiales is a group of asexual, unicellular red algae, which thrive in acidic and high temperature conditions around hot springs. These unicellular taxa have a relatively simple morphology and are currently classified into three genera, Cyanidium, Cyanidioschyzon and Galdieria. Little is known, however, about the biodiversity of Cyanidiales, their population structure and their phylogenetic relationships. Here we used a taxonomically broadly sampled three-gene data set of plastid sequences to infer a robust phylogenetic framework for the Cyanidiales. The phylogenetic analyses support the existence of at least four distinct Cyanidiales lineages: the Galdieria spp. lineage (excluding Galdieria maxima), the Cyanidium caldarium lineage, a novel monophyletic lineage of mesophilic Cyanidium spp. and the Cyanidioschyzon merolae plus Galdieria maxima lineage. Our analyses do not support the notion of a mesophilic ancestry of the Cyanidiales and suggest that these algae were ancestrally thermo-acidotolerant. We also used environmental polymerase chain reaction (PCR) for the rbcL gene to sample Cyanidiales biodiversity at five ecologically distinct sites at Pisciarelli in the Phlegrean Fields in Italy. This analysis showed a high level of sequence divergence among Cyanidiales species and the partitioning of taxa based on environmental conditions. Our research revealed an unexpected level of genetic diversity among Cyanidiales that revises current thinking about the phylogeny and biodiversity of this group. We predict that future environmental PCR studies will significantly augment known biodiversity that we have discovered and demonstrate the Cyanidiales to be a species-rich branch of red algal evolution.     

Effects of variation at the flower-colour A locus on mating system parameters in Ipomoea purpurea

Although alleles at both the W and A loci in the common morning glory, Ipomoea purpurea, produce similar white-flowered phenotypes, these alleles differ by over an order of magnitude in average frequency. In this initial attempt to determine the causes of this difference, we employed artificial arrays of plants to estimate mating system characteristics (total siring success, selfing rates and contribution to the outcross pollen pool) for the homozygous pigmented and white-flowered genotypes at the A locus. This experiment demonstrates that: (1) at both low and high frequencies, white-flowered plants were visited by pollinators at the same rate as plants with pigmented flowers; (2) at both frequencies, the a allele exhibited a greater total siring success (self and outcross pollen) than the A allele; (3) individuals of both genotypes contributed equally to the outcross pollen pool; and (4) aa plants may have a higher selfing rate than AA plants. Coupled with minimal inbreeding depression in I. purpurea, these observations indicate that the allele producing white flowers enjoys a transmission advantage that would tend to cause this allele to increase in frequency. This transmission advantage is very similar to that shown previously to be operating on the white-flowered allele at the W locus, although the specific causes of the advantage appear to differ between loci. The frequency difference between the two alleles is thus not likely to be due to differences in the effect of flower-colour variation on transmission. Rather, substantially greater deleterious pleiotropic effects associated with the white-flower a allele is likely to be the primary cause of the frequency difference.     

Extrapair paternity in the blue tit (Parus caeruleus) : female choice, male charateristics, and offspring quality

Extrapair paternity is common in many birds, and it is now generallyaccepted that female choice plays an important role. However,die benefits that females obtain from extrapair paternity aremuch less dear. To test the hypothesis that females obtain indirectfitness benefits, we studied paternity in a blue tit populationover 4 years. Extrapair paternity occurred in 31-47% of allnests and accounted for 11-14% of all offspring. Most malesthat fathered extrapair young did not lose paternity themselves,males never "exchanged" paternity, and within nests the extrapairoffspring were usually fathered by a single male. Comparisonsbetween males that did and did not lose paternity and pairwisecomparisons between the extrapair male(s) and the within-pairmale showed that successful males had longer tarsi and sangon average longer strophes during the dawn chorus. Successfulmales weighed less (relative to their size) during the nettlingstage, but nevertheless they survived better. Male age did notinfluence their likelihood of losing paternity, but extrapairmales were usually older than the within-pair male they cuckolded.Within nests with mixed paternity, extrapair young were morelikely to survive than within-pair young in cases of partialbrood mortality. Our data also suggest that extrapair offspringwere more likely to be males. Because extrapair males were usuallyclose neighbors, male quality should be considered relativeto the quality of the neighbors. Despite this, we found consistencyin female choice over years. Our observations provide supportfor the hypothesis that female blue tits engage in extrapaircopulations to obtain good genes for their offspring.     

Chromosomal Mapping of Genes in theRBCS Family in Arabidopsis thaliana

In Arabidopsis thaliana, four genes have been identified inthe RBCS gene family, one being assigned to subfamily RBCS-Aand the other three to subfamily RBCS-B (1B, 2B and 3B). Todetermine the chromosomal location ofthese genes, hybridizationanalysis with CIC YAC high-density filters was carried out forthe RBCS-A gene, and CAPS analysis for the three RBCS-B genes,based on the finding that restriction fragment length polymorphismis present in the upstream region of the gene RBCS-3B. The RBCS-Agene was mapped at 100.8 cM from the top of chromosome 1 andthe three RBCS-B genes at 62.70 cM from the top of chromosome5.     

Quox-1基因同源序列在人胚早期发育中的表达

以Quox-1基因的特异性片段b_2为探针,与人基因组DNA作Southern杂交,结果显示,人基因组中存在Quox-1基因的同源序列。以抗Quox-1蛋白的抗体与早期人胚胎组织的切片作免疫组化反应研究了Quox-1基因同源序列在人胚早期发育过程中的表达,结果表明其表达有明显的时间和空间特异性。胚龄30天以前,Quox-1基因的同源序列在人胚包括神经管等许多部位表达,30天以后表达部位局限于脊索、心肌细胞、生肌节、消化道上皮及周皮等处。文中讨论了Quox-1基因同源顺序对人类胚胎早期发育过程可能的调控作用。