FRIGIDA-independent variation in flowering time of natural Arabidopsis thaliana accessions

FRIGIDA (FRI) and FLOWERING LOCUS C (FLC) are two genes that, unless plants are vernalized, greatly delay flowering time in Arabidopsis thaliana. Natural loss-of-function mutations in FRI cause the early flowering growth habits of many A. thaliana accessions. To quantify the variation among wild accessions due to FRI, and to identify additional genetic loci in wild accessions that influence flowering time, we surveyed the flowering times of 145 accessions in long-day photoperiods, with and without a 30-day vernalization treatment, and genotyped them for two common natural lesions in FRI. FRI is disrupted in at least 84 of the accessions, accounting for only approximately 40% of the flowering-time variation in long days. During efforts to dissect the causes for variation that are independent of known dysfunctional FRI alleles, we found new loss-of-function alleles in FLC, as well as late-flowering alleles that do not map to FRI or FLC. An FLC nonsense mutation was found in the early flowering Van-0 accession, which has otherwise functional FRI. In contrast, Lz-0 flowers late because of high levels of FLC expression, even though it has a deletion in FRI. Finally, eXtreme array mapping identified genomic regions linked to the vernalization-independent, late-flowering habit of Bur-0, which has an alternatively spliced FLC allele that behaves as a null allele.     

Needle track seeding of papillary thyroid carcinoma from fine needle aspiration biopsy. A case report

BACKGROUND: Dissemination of tumor cells from needle biopsy has been observed in a wide range of tumor types. Fine needle aspiration (FNA) biopsy has become accepted as the first-line test in the evaluation of thyroid nodules. Local recurrence of thyroid cancer from needle track seeding is an extremely rare complication of thyroid FNA. CASE: A 59-year-old woman developed local recurrence of papillary thyroid carcinoma three years after FNA of the primary cancer. Local metastases developed in the skin and sternocleidomastoid muscle. The location of the recurrent cancer and the linear relationship of the metastases indicated that local recurrence was due to needle track seeding at the time of FNA. CONCLUSION: Needle track seeding has been recognized as a possible, albeit rare, complication of FNA of thyroid cancer. Although proper FNA technique can reduce the potential for needle track seeding, its occurrence is an unavoidable complication of FNA evaluation of thyroid malignancies.     

Molecular analysis of an anion pump: purification of the ArsC protein.

The ars operon of resistance plasmid R773 encodes an anion-translocating ATPase which catalyzes extrusion of the oxyanions arsenite, antimonite, and arsenate, thus providing resistance to the toxic compounds. Although both arsenite and arsenate contain arsenic, they have different chemical properties. In the absence of the arsC gene the pump transports arsenite and antimonite, oxyanions with the +III oxidation state of arsenic or antimony. The complex neither transports nor provides resistance to arsenate, the oxyanion of the +V oxidation state of arsenic. The arsC gene encodes a 16-kDa polypeptide, the ArsC protein, which alters the substrate specificity of the pump to allow for recognition and transport of the alternate substrate arsenate. The arsC gene was cloned behind a strong promoter and expressed at high levels. The ArsC protein was purified and crystallized.     

The Arabidopsis thaliana MERISTEM LAYER 1 promoter specifies epidermal expression in meristems and young primordia

The Arabidopsis thaliana MERISTEM LAYER 1 (ATML1) gene is expressed in the epidermis of developing embryos and shoot meristems. To identify regulatory sequences necessary for epidermis-specific expression, three fusions of overlapping ATML1 genomic sequences to the GUS reporter gene were introduced into Arabidopsis plants. All fusion genes conferred epidermis-specific expression of both GUS mRNA and protein activity but varied in both the timing and relative levels of expression, suggesting partial redundancy of ATML1 regulatory elements. This study defines L1-specific regulatory sequences that are sufficient to direct foreign gene expression in a layer-specific manner.     

Plastocyanin is indispensable for photosynthetic electron flow in Arabidopsis thaliana

Plastocyanin is a soluble copper-containing protein present in the thylakoid lumen, which transfers electrons to photosystem I. In the chloroplast of the flowering plant Arabidopsis thaliana, a cytochrome c6-like protein is present, which was recently suggested to function as an alternative electron carrier to plastocyanin. We show that Arabidopsis plants mutated in both of the two plastocyanin-coding genes and with a functional cytochrome c6 cannot grow photoautotrophically because of a complete block in light-driven electron transport. Even increased dosage of the gene encoding the cytochrome c6-like protein cannot complement the double mutant phenotype. This demonstrates that in Arabidopsis only plastocyanin can donate electrons to photosystem I in vivo.     

Quantitative trait loci controlling light and hormone response in two accessions of Arabidopsis thaliana

We have mapped quantitative trait loci (QTL) responsible for natural variation in light and hormone response between the Cape Verde Islands (Cvi) and Landsberg erecta (Ler) accessions of Arabidopsis thaliana using recombinant inbred lines (RILs). Hypocotyl length was measured in four light environments: white, blue, red, and far-red light and in the dark. In addition, white light plus gibberellin (GA) and dark plus the brassinosteroid biosynthesis inhibitor brassinazole (BRZ) were used to detect hormone effects. Twelve QTL were identified that map to loci not previously known to affect light response, as well as loci where candidate genes have been identified from known mutations. Some QTL act in all environments while others show genotype-by-environment interaction. A global threshold was established to identify a significant epistatic interaction between two loci that have few main effects of their own. LIGHT1, a major QTL, has been confirmed in a near isogenic line (NIL) and maps to a new locus with effects in all light environments. The erecta mutation can explain the effect of the HYP2 QTL in the blue, BRZ, and dark environments, but not in far-red. LIGHT2, also confirmed in an NIL, has effects in white and red light and shows interaction with GA. The phenotype and map position of LIGHT2 suggest the photoreceptor PHYB as a candidate gene. Natural variation in light and hormone response thus defines both new genes and known genes that control light response in wild accessions.     

Glycans as endocytosis signals: the cases of the asialoglycoprotein and hyaluronan/chondroitin sulfate receptors

Animal cells internalize specific extracellular macromolecules (ligands) by using specialized cell surface receptors that operate through a complex and highly regulated process known as receptor-mediated endocytosis, which involves the binding, internalization, and transfer of ligands through a series of distinct intracellular compartments. For the uptake of a variety of carbohydrate-containing macromolecules, such as glycoproteins, animal cells use specialized membrane-bound lectins as endocytic receptors that recognize different sugar residues or carbohydrate structures present on various ligands. The hepatic asialoglycoprotein receptor, which recognizes glycoconjugates containing terminal galactose or N-acetylgalactosamine residues, was the first membrane lectin discovered and has been a classical system for studying receptor-mediated endocytosis. Studies of how the asialoglycoprotein receptor functions have led to the discovery of two functionally distinct, parallel pathways of clathrin-mediated endocytosis (called the State 1 and State 2 pathways), which may also be utilized by all the other endocytic recycling receptor systems. Another endocytic membrane lectin, the hyaluronan/chondroitin sulfate receptor, which has recently been purified and cloned, is responsible for the turnover in mammals of these glycosaminoglycans, which are important components of extracellular matrices. We discuss the characteristics and physiological importance of these two proteins as examples of how lectins can function as endocytic receptors.     

Regulation of auxin response by the protein kinase PINOID

Arabidopsis plants carrying mutations in the PINOID (PID) gene have a pleiotropic shoot phenotype that mimics that of plants grown on auxin transport inhibitors or of plants mutant for the auxin efflux carrier PINFORMED (PIN), with defects in the formation of cotyledons, flowers, and floral organs. We have cloned PID and find that it is transiently expressed in the embryo and in initiating floral anlagen, demonstrating a specific role for PID in promoting primordium development. Constitutive expression of PID causes a phenotype in both shoots and roots that is similar to that of auxin-insensitive plants, implying that PID, which encodes a serine-threonine protein kinase, negatively regulates auxin signaling.