Abstract
Adventitious rooting plays an important role in the commercial vegetative propagation of trees. Adventitious root formation is a complex biological process, but knowledge of the possible unintended effects induced by both the integration/expression of transgenes and in vitro conditions on the rooting is limited. The long-term stability of transgene expression is important both for original transformants of woody plants and its progeny. In this study, we used field-grown pear rootstock GP217 trees transformed with the reporter ß-glucuronidase (uidA) genes with and without intron and re-transformed with the herbicide resistance bar gene as model systems. We assessed the unintended effects on rooting of pear semi-hardwood cuttings and evaluated the stability of transgene expression in progeny produced by generative (seedlings) and vegetative (grafting, cutting) means up to four years. Our investigation revealed that: (1) The single and repeated transformations of clonal pear rootstocks did not result in unintended effects on adventitious root formation in cuttings; (2) stability of the transgene expression was confirmed on both generative and vegetative progeny, and no silenced transgenic plants were detected; (3) yearly variation in the gene expressions was observed and expression levels were decreased in extremely hot and dry summer; (4) the intron enhanced the expression of uidA gene in pear plants approximately two-fold compared to gene without intron. The current study provides useful information on transgene expression in progeny of fruit trees under natural environmental conditions.
Highlights
Pear is one of the most important fruit species in the temperate-zone countries
Rooting of transgenic shoots on the medium supplemented with the appropriate selective antibiotic or herbicide showed that significant differences were observed between the lines carrying the uidA-intron gene on the medium with hygromycin (Table 1)
Adventitious rooting is used for the reproduction of most fruit and forest tree species as one of the cheapest and simplest methods of vegetative propagation, as well as clonal micropropagation
Summary
Pear is one of the most important fruit species in the temperate-zone countries (temperate climate zone). Breeding of new genotypes of pears is carried out both by classical methods: Hybridization (in the last several centuries) or mutation techniques Whatever method is used to develop new cultivars, they need to be propagated in large quantities for commercial use. As the majority of horticultural crops, the pear is propagated by vegetative means for obtaining genetically uniform plants, whereas the sexual propagation is used by breeders. Among vegetative propagation methods, including budding, grafting, layering and cuttings, stem cutting is the most effective and economical method for producing large quantities of plants without altering the genetic constitution, especially fruit and forest trees [5,6].
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