Due to the rising public concern over the use of genes conferring antibiotic and herbicide resistance, alternative systems for selection after plant transformation are being developed. A positive selection system consists of a physiologically inert metabolite as the selection agent and a respective gene which determines a metabolic advantage via selection agent utilization. The transformed cells are able to overcome the suppressive effects of the selection, while the untransformed ones starve but are not killed. The enzyme phosphomannose isomerase (PMI, E.C. 5.3.1.8) catalyzes the reversible interconversion of mannose-6-phosphate and fructose-6-phosphate in prokaryotic and eukaryotic organisms. The PMI selection system is called positive due to the effect of ''starvation'' caused to the nontransformed plant tissue because of its incapability to utilize mannose as a carbon source. In this mini-review we researched the literature to obtain a more detailed view of the characteristics, specifics, problems, and advantages of applying the PMI/mannose selection system.
Members of the glycogen synthase kinase 3/SHAGGY-like protein kinase (GSK) family in plants are important regulators of stress response, development, and brassinosteroid signaling, and are highly homologous to animal GSKs. Several of the plant kinases are preferentially expressed during pollen development. We report the characterization of LpSK6, a member of the GSK family from the genus Lycopersicon. LpSK6 shows high sequence homology to members of group III, which contain a putative mitochondrial targeting peptide. LpSK6 is expressed 3 to 5 fold higher in anthers than in roots and stems, and is the first GSK gene isolated from genus Lycopersicon.
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