Pleiotropic Trait Research Articles

Pleiotropy of pea RisfixC supernodulation mutation is symbiosis-independent

Mutations affecting the development of root symbiosis between legume plants (Fabaceae) and nodule bacteria (rhizobia) are often associated with pleiotropy. This might either primarily be caused by the mutation or develops as a physiological consequence of a changed nodule structure, number and activity. Three pleiotropic traits were revealed in the pea (Pisum sativum L.) mutant RisfixC which is of supernodulation/nitrate-tolerant symbiosis (Nts) type. They comprise shortened internodes, reduced shoot dry mass accumulation and increased nitrogen content in the root tissues when compared to the wild type. The changes were expressed in the same degree in asymbiotic and nodulated plants when the effect of symbiotic nitrogen on plant growth was abolished with a saturating nitrate level. Consequently, the pleiotropic traits are inherently associated with the mutation. In RisfixC, the pleiotropy coincided with the presumed absence of the systemic feedback factor regulating nodule number. However, no differences were detected in the comparison of nonnodulating mutant Risnod27 (sym8) with the wild type and of inoculated with noninoculated wild-type plants although these pairs also differ in the presence of the systemic factor. Therefore, the pathway leading from the RisfixC mutant product to pleiotropic changes appears to be independent of systemic nodule number regulation. Implications for the genetic improvement of growth and yield parameters of supernodulating breeding lines are discussed.

Accumulation of trehalose within transgenic chloroplasts confers drought tolerance

Yeast trehalose phosphate synthase(TPS1) gene was introduced into the tobacco chloroplast ornuclear genomes to study resultant phenotypes. PCR and Southern blots confirmedstable integration of TPS1 into the chloroplast genomes ofT1, T2 and T3 transgenic plants. Northern blotanalysis of transgenic plants showed that the chloroplast transformantexpressed169-fold more TPS1 transcript than the best survivingnuclear transgenic plant. Although both the chloroplast and nuclear transgenicplants showed significant TPS1 enzyme activity, no significant trehaloseaccumulation was observed in T0/T1 nuclear transgenicplants whereas chloroplast transgenic plants showed 15–25 fold higheraccumulation of trehalose than the best surviving nuclear transgenic plants.Nuclear transgenic plants (T0) that showed even small amounts oftrehalose accumulation showed stunted phenotype, sterility and otherpleiotropiceffects whereas chloroplast transgenic plants (T1, T2,T3) showed normal growth and no pleiotropic effects. Transgenicchloroplast thylakoid membranes showed high integrity under osmotic stress asevidenced by retention of chlorophyll even when grown in 6% PEG whereaschloroplasts in untransformed plants were bleached. After 7 hrdrying, chloroplast transgenic seedlings (T1, T3)successfully rehydrated while control plants died. There was no differencebetween control and transgenic plants in water loss during dehydration butdehydrated leaves from transgenic plants (not watered for 24 days) recoveredupon rehydration turning green while control leaves dried out. Theseobservations suggest that trehalose functions by protecting biologicalmembranesrather than regulating water potential. In order to prevent escape of droughttolerance trait to weeds and associated pleiotropic traits to related crops, itmay be desirable to engineer crop plants for drought tolerance via thechloroplast genome instead of the nuclear genome.

RtpA, a gene encoding a bacterial two-component sensor kinase, determines pathogenic traits of Pseudomonas tolaasii, the causal agent of brown blotch disease of a cultivated mushroom, Pleurotus ostreatus

Pseudomonas tolaasii strain PT814 produces extracellular toxins, tolaasins, and a volatile toxin, tovsin, that are responsible for the induction of brown blotch and rotting, respectively, in a cultivated mushroom, Pleurotus ostreatus. Insertions of single transposon mini-Tn 5km 1 into the chromosome of P. tolaasii strain PT814 generated mutants that are pleiotropically defective in tolaasin and protease production, and altered in colony morphology. The mutants, however, produce tovsin at the level of wild-type. Variants phenotypically similar to the pleiotropic mutants of P. tolaasiistrain PT814 spontaneously occurred in P. tolaasii strain S8501 at 22–30°C in vitro. The occurrence of variants was significantly reduced in the presence of extracts of P. ostreatus or at a temperature of 15–20°C The rtpA gene (rtpA = regulator gene of tolaasin production and other pleiotropic traits) isolated from a P. tolaasii strain PT814 gene library restored the wild-type phenotype in both the mini-Tn5 km 1 insertion and spontaneous mutants, mini-Tn5 km 1 insertions were also located in the allele of rtpA. Nucleotide sequencing of the rtpA DNA revealed an open reading frame of 2,751 bp predicted to encode a protein consisting of 917 amino acid residues with a molecular mass of 100.6 kDa and displaying the conserved amino acid sequence of both sensor and receiver domains of “bacterial two-component regulators.” The data suggest that the machinery responding to environmental stimuli is essential for the pathogenic interaction of P. tolaasii with the mushroom.

A unique bilirubin-UDP-glucuronosyltransferase deficiency related to neonatal jaundice in mice.

This report describes biochemical and cellular characterization of a spontaneous mutation in ICR mice; the mutation has been phenotypically characterized as autosomal recessive jaundice in neonates and juveniles and given the gene symbol hub (J. Hered. 76:441-446, 1985; Mouse Newslett. 73:28, 1985). The results obtained demonstrate that (1) mice homozygous for the mutation are deficient in bilirubin-UDP-glucuronosyltransferase activity, and there is no deficiency in heterozygous mice, (2) the deficiency is lifelong, even though the clinical symptom of jaundice is transitory and restricted to neonates or juveniles, (3) bilirubin-UDP-glucuronosyltransferase activity in mutant and nonmutant mice is similarly induced by triiodothyronine, (4) glucuronidation and xylodation of bilirubin probably occur as the result of separate enzyme forms in mice, and (5) Western analysis using antibody to rat bilirubin-UDP-glucuronosyltransferase indicates that although there is no electrophoretic mobility difference, there is a diffuse band missing in mutant mice. Hepatic hyperplasia, cytomegaly, single-cell necrosis, and eosinophilic foci are also pleiotropic traits associated with homozygous but not heterozygous hub. The hub/hub mouse will be useful in the study of substrate specificity and regulation within a complex gene family and, perhaps, provide a new and useful animal model for the long-term health effects of deficiency in the metabolism of xenobiotics cleared via UDP-glucuronosyltransferase.