PROLIFERATING INFLORESCENCE MERISTEM,a MADS-box gene that regulates floral meristem identity in pea

SQUAMOSA and APETALA1 are floral meristem identity genes from snapdragon (Antirrhinum majus) and Arabidopsis, respectively. Here, we characterize the floral meristem identity mutation proliferating inflorescence meristem (pim) from pea (Pisum sativum) and show that it corresponds to a defect in the PEAM4 gene, a homolog of SQUAMOSA and APETALA1. The PEAM4 coding region was deleted in the pim-1 allele, and this deletion cosegregated with the pim-1 mutant phenotype. The pim-2 allele carried a nucleotide substitution at a predicted 5' splice site that resulted in mis-splicing of pim-2 mRNA. PCR products corresponding to unspliced and exon-skipped mRNA species were observed. The pim-1 and pim-2 mutations delayed floral meristem specification and altered floral morphology significantly but had no observable effect on vegetative development. These floral-specific mutant phenotypes and the restriction of PIM gene expression to flowers contrast with other known floral meristem genes in pea that additionally affect vegetative development. The identification of PIM provides an opportunity to compare pathways to flowering in species with different inflorescence architectures.     

Mapping of the nodulation loci sym9 and sym10 of pea ( Pisum sativum L.)

Several mutants defective in the nodulation process during rhizobial or endomycorrhizal endosymbiosis of pea have been identified previously. We have integrated the map positions of two such nodulation mutations, sym9 and sym10, into the molecular map of pea by applying molecular-marker techniques combined with bulked segregant analysis (BSA). Lines P2 and P54 were found to carry alleles of sym9, line P56 carried an allele of sym10. F2 populations were derived from crosses of P2, P54 and P56, to JI281 and JI15, two of the parental lines that have been used previously to generate a molecular map of pea. sym9 was located on linkage group IV by AFLP-BSA analysis and subsequently mapped by RFLP in both F2 populations, P2 2 JI281 and P54 2 JI281. RFLP-BSA analysis was applied to assign sym10 to linkage group I. The RFLP marker locus, chs2, co-segregates with sym10 in the F2 population of P56 2 JI15.     

CYP98A6 from Lithospermum erythrorhizon encodes 4-coumaroyl-4'-hydroxyphenyllactic acid 3-hydroxylase involved in rosmarinic acid biosynthesis

Rosmarinic acid is the dominant hydroxycinnamic acid ester accumulated in Boraginaceae and Lamiaceae plants. A cytochrome P450 cDNA was isolated by differential display from cultured cells of Lithospermum erythrorhizon, and the gene product was designated CYP98A6 based on the deduced amino acid sequence. After expression in yeast, the P450 was shown to catalyze the 3-hydroxylation of 4-coumaroyl-4'-hydroxyphenyllactic acid, one of the final two steps leading to rosmarinic acid. The expression level of CYP98A6 is dramatically increased by addition of yeast extract or methyl jasmonate to L. erythrorhizon cells, and its expression pattern reflected the elicitor-induced change in rosmarinic acid production, indicating that CYP98A6 plays an important role in regulation of rosmarinic acid biosynthesis.     

Muscular dystrophies, dilated cardiomyopathy, lipodystrophy and neuropathy: the nuclear connection

An understanding of muscle structure and function is central to improving our knowledge of the group of muscle diseases referred to as muscular dystrophies. These diseases involve a progressive weakening and wasting of skeletal muscle, which can be associated with life-threatening cardiac arrhythmias. The vast majority of these diseases arise from defects in either cytoskeletal or structural proteins, resulting in a breakdown of muscle cell integrity. However, mutations in two nuclear proteins--emerin and lamin A/C--have also been demonstrated to give rise to a muscular dystrophy phenotype. In addition, mutations in lamin A/C can give rise to a dilated cardiomyopathy, a lipodystrophy or a neuropathy. It is far from clear how mutations in nuclear proteins can result in a dystrophy, or cause more than one clinically distinct disease. Understanding the functional role of nuclear proteins in causing these diseases will therefore provide novel insights into muscle function, and should hopefully provide new directions for treatment.     

aph-1 and pen-2 are required for Notch pathway signaling,gamma-secretase cleavage of betaAPP,and presenilin protein accumulation

Presenilins are components of the gamma-secretase protein complex that mediates intramembranous cleavage of betaAPP and Notch proteins. A C. elegans genetic screen revealed two genes, aph-1 and pen-2, encoding multipass transmembrane proteins, that interact strongly with sel-12/presenilin and aph-2/nicastrin. Human aph-1 and pen-2 partially rescue the C. elegans mutant phenotypes, demonstrating conserved functions. The human genes must be provided together to rescue the mutant phenotypes, and the inclusion of presenilin-1 improves rescue, suggesting that they interact closely with each other and with presenilin. RNAi-mediated inactivation of aph-1, pen-2, or nicastrin in cultured Drosophila cells reduces gamma-secretase cleavage of betaAPP and Notch substrates and reduces the levels of processed presenilin. aph-1 and pen-2, like nicastrin, are required for the activity and accumulation of gamma-secretase.     

Protein folding and misfolding inside and outside the cell.

The workshop was held at St Catherine's College, Oxford, from March 25-28, 1998, and attracted participants from 32 nations. Protein folding is one of the most important processes in biology since it adds functional flesh to the bare bones of genes, but it has traditionally been studied by people separated both intellectually and physically because they are training in different disciplines. The aim of the meeting was to bring together chemists and structural biologists studying how pure, denatured proteins refold spontaneously in the test tube, with biochemists and cell biologists who are concerned with how proteins fold inside living cells and medical scientists interested in the diseases that result when this process goes wrong. In this report we concentrate on general concepts and themes rather than on detailing every contribution.     

Polymorphism of insertion sites of Ty1-copia class retrotransposons and its use for linkage and diversity analysis in pea

A sample of 15 cultivars and 56 Pisum accessions from the JIC germplasm core collection has been studied using a modification of the SSAP (sequence-specific amplification polymorphisms) technique; the specific primer was designed to correspond to the polypurine tract (PPT) of PDR1, a Ty1-copia group retrotransposon of pea. Most of these SSAP products were shown to be PDR1 derived. The PDR1 SSAP markers are more informative than previously studied AFLP or RFLP markers and are distributed throughout the genome. Their pattern of variation makes them ideal for integrating genetic maps derived from related crosses. Data sets obtained with AFLP and PDR1 SSAP markers were used to construct neighbour-joining trees and for principal component analysis. These data sets give greater resolution than hitherto available for the characterisation of variation within Pisum, showing that the genus has three main groups: P. fulvum, P. abyssinicum and all other Pisum spp. P. abyssinicum is not a subgroup of cultivated P. sativum, as was previously thought, but has probably been domesticated independently. Modern cultivars are shown to form a single group within Pisum as a whole. Received: 21 April 1998 / Accepted: 9 June 1998     

Genetic mapping in pea. 1. RAPD-based genetic linkage map of Pisum sativum

 A genetic linkage map of Pisum sativum L. was constructed based primarily on RAPD markers that were carefully selected for their reproducibility and scored in a population of 139 recombinant inbred lines (RILs). The mapping population was derived from a cross between a protein-rich dry-seed cultivar ‘Térèse’ and an increased branching mutant (K586) obtained from the pea cultivar ‘Torsdag’. The map currently comprises nine linkage groups with two groups comprising only 6 markers (n=7 in pea) and covers 1139 cM. This RAPD-based map has been aligned with the map based on the (JI281×JI399) RILs population that currently includes 355 markers in seven linkage groups covering 1881 cM. The difference in map lengths is discussed. For this alignment 7 RFLPs, 23 RAPD markers, the morphological marker le and the PCR marker corresponding to the gene Uni were used as common markers and scored in both populations. Received: 13 March 1998 / Accepted: 29 April 1998     

Human hydrometry: comparison of multifrequency bioelectrical impedance with 2H2O and bromine dilution

The traditionalmethod of assessing total body water (TBW), extracellular water (ECW),and intracellular water (ICW) has been the use of isotopes, on thebasis of the dilution principle. Although the development ofbioelectrical impedance techniques has eliminated many of themeasurement constraints associated with the dilution methods, thedegree of interchangeability between the two methods remains uncertain.We used multifrequency bioelectrical impedance spectroscopy (BIS),²H₂Odilution, and bromine dilution to assess TBW, ECW, and ICW in 469 healthy subjects (248 males, 221 females) aged 3-29 yr. We foundthat the TBW, ECW, and ICW estimates for the BIS and dilution methodswere significantly correlated(r² = 0.80-0.96, P < 0.0001, SE ofthe estimate = 2.3-2.7 liters). On the basis of population, theconstants used in the BIS analysis could be adjusted so that the meandifferences with the dilution methods would become zero. The SD valuesfor the mean differences between the dilution and BIS methods, however,remained significant for both males and females: TBW (±2.1-2.8liters), ECW (±1.4-1.6 liters), and ICW (2.0-3.1 liters).To improve the accuracy of the BIS measurement for an individual withinthe age range we have examined, further refinement of the constantsused in the BIS analysis is needed.