ABSTRACT
Two S-adenosylmethionine synthetase (SAMS) cDNAs, PcSAMS1 and PcSAMS2, have been identified in Pinus contorta. We found that the two genes are differentially expressed during root development. Thus, PcSAMS1 is preferentially expressed in roots and exhibits a specific expression pattern in the meristem at the onset of adventitious root development, whereas PcSAMS2 is expressed in roots as well as in shoots and is down-regulated during adventitious root formation. The expression of the two SAMS genes is different from the SAMS activity levels during adventitious root formation. We conclude that other SAMS genes that remain to be characterized may contribute to the observed SAMS activity, or that the activities of PcSAMS1 and PcSAMS2 are affected by post-transcriptional regulation. The deduced amino acid sequences of PcSAMS1 and PcSAMS2 are highly divergent, suggesting different functional roles. However, both carry the two perfectly conserved motifs that are common to all plant SAMS. At the protein level, PcSAMS2 shares about 90% identity to other isolated eukaryotic SAMS, while PcSAMS1 shares less than 50% identity with other plant SAMS. In a phylogenetic comparison, PcSAMS1 seems to have diverged significantly from all other SAMS genes. Nevertheless, PcSAMS1 was able to complement a Saccharomyces cerevisiae sam1 sam2 double mutant, indicating that it encodes a functional SAMS enzyme.
Subject(s)
Cycadopsida/genetics , Methionine Adenosyltransferase/genetics , Plant Roots/genetics , Amino Acid Sequence , Cycadopsida/enzymology , Cycadopsida/growth & development , DNA, Complementary/chemistry , DNA, Complementary/genetics , Gene Expression Regulation, Developmental , Gene Expression Regulation, Enzymologic , Gene Expression Regulation, Plant , Genetic Complementation Test , Hypocotyl/drug effects , Hypocotyl/enzymology , Hypocotyl/genetics , In Situ Hybridization , Indoleacetic Acids/pharmacology , Indoles/pharmacology , Isoenzymes/genetics , Isoenzymes/metabolism , Methionine Adenosyltransferase/metabolism , Molecular Sequence Data , Mutation , Phylogeny , Plant Roots/drug effects , Plant Roots/growth & development , RNA, Messenger/drug effects , RNA, Messenger/genetics , RNA, Messenger/metabolism , Saccharomyces cerevisiae/genetics , Sequence Alignment , Sequence Analysis, DNA , Sequence Homology, Amino Acid , Tissue Distribution , Transcription, GeneticABSTRACT
Auxin stimulated rooting of epicotyl cuttings of Pinus sylvestris irrespective of the physiological stage of the plant from which the cuttings were taken. The epicotyl cuttings were divided into two groups, those that differentiated roots early (within 6 weeks after cutting) and those that differentiated roots late (more than 6 weeks after cutting). Auxin treatment significantly stimulated the frequency of early rooting of epicotyl cuttings, whereas it had no effect on the frequency of late rooting of epicotyl cuttings. The number of roots per rooted cutting was significantly higher after auxin treatment both on early and late rooted cuttings. Anatomical studies showed that most of the roots on both early and late rooted cuttings developed from wound tissue. However some types of rooting were found only after auxin treatment of early rooted cuttings, e.g., roots that developed from resin duct wound tissue or from vascular tissue or in the pith.
