RYS1, a foldback transposon, is activated by tissue culture and shows preferential insertion points into the rye genome.

The study of two variable amplicons of rye indicates that RYS1, a mobile element, is activated during tissue culture. We propose that RYS1 could be a foldback (FB) transposon. The FB transposons have been rarely reported in plants; RYS1 is the first described in rye and also the first active plant FB transposon reported. Preferential integration points in the rye genome exist, because the new insertions seem to be located, in all studied cases, in the same genome positions. We assume that RYS1 became active in rye very recently, as different plants from in vivo-growing cultivars showed that these elements were present or absent in the same genomic position in which the in vitro-activated element was found. This high rate of modification in these particular loci, both in the in vivo and in vitro populations, could indicate that probably the mechanisms promoting genetic variability in nature are the same that induce variation in vitro, and the modifications induced by somaclonal variation could be already present in vivo populations.

Expression of different abscisic acid-responsive genes during somatic embryogenesis in sugarcane (Saccharum officinarum).

We have examined the expression of four genes during somatic embryogenesis in two cultivars of sugarcane, Saccharum officinarum, one drought resistant (JA-605) and the other one sensitive (C-8751), as well as in embryogenic and nonembryogenic tissues treated with abscisic acid (ABA) or after drought stress. Three of the cDNAs probed, from plasmids pMA1049, pMA2005 and CM1, were lea genes and the other one, from a barley hemoglobin gene, was induced in other species under stress conditions. Only transcripts homologous to the pMA2005 and CM1 clones were differentially accumulated during somatic embryogenesis; moreover, the CM1 clone only appeared in somatic embryos of the non-resistant variety. All the lea cDNAs were dramatically increased in the embryogenic tissues treated with ABA, but we observed differences among the accumulation of these mRNAs in the nonembryogenic tissues treated with ABA, and only the pMA2005 transcript appeared. The mRNA homologous to the barley hemoglobin gene appeared in the nonembryogenic tissue and the expression increased after ABA treatment. The desiccation treatments had different effects on the varieties, and the pMA2005 transcripts only appeared in the sensitive variety.

Analysis of T-DNA-mediated translational beta-glucuronidase gene fusions.

Three random translational beta-glucuronidase (gus) gene fusions were previously obtained in Arabidopsis thaliana, using Agrobacterium-mediated transfer of a gus coding sequence without promoter and ATG initiation site. These were analysed by IPCR amplification of the sequence upstream of gus and nucleotide sequence analysis. In one instance, the gus sequence was fused, in inverse orientation, to the nos promoter sequence of a truncated tandem T-DNA copy and translated from a spurious ATG in this sequence. In the second transgenic line, the gus gene was fused to A. thaliana DNA, 27 bp downstream an ATG. In this line, a large deletion occurred at the target site of the T-DNA. In the third line, gus is fused in frame to a plant DNA sequence after the eighth codon of an open reading frame encoding a protein of 619 amino acids. This protein has significant homology with animal and plant (receptor) serine/threonine protein kinases. The twelve subdomains essential for kinase activity are conserved. The presence of a potential signal peptide and a membrane-spanning domain suggests that it may be a receptor kinase. These data confirm that plant genes can be tagged as functional translational gene fusions.

Somaclonal variation in rye.

We studied the genetic variation generated during in vitro culture of rye Secale cereale L. We analyzed the progenies of four generations of the plants regenerated from immature embryo cultures. A high frequency of mutant plants was observed, 50.75%, this frequency was genotype dependent. Other characteristics typical of somaclonal variation were also observed: the obtaining of dominant mutations, the presence of more than one mutation per plant, the obtaining of homozygous mutants and a high rate of mutation of particular loci. In some cases transposable elements could be implicated. We postulate that tissue culture could induce mutations as well as select particular cell types and so increase the appearance of special mutants.

Somatic embryogenesis in polyembryonic Secale cereale L.

The progeny of polyembryonic Secale cereale L., was used to study the in vitro response of the immature embryos. The formation of embryogenic calli was very high, and this response and its distribution was statistically different to that shown by the normal regenerated plants and the original population. This behaviour seems to be related to a genetic condition which favours the presence of supernumerary embryos, in vivo as well as in vitro.