Abstract
Metal hyperaccumulating plants are able to store very large amounts of metals in their shoots. There are a number of reasons why it is important to be able to introduce metal hyperaccumulation traits into non-accumulating species (e.g., phytoremediation or biofortification in minerals) and to engineer a desired level of accumulation and distribution of metals. Metal homeostasis genes have therefore been used for these purposes. Engineered accumulation levels, however, have often been far from expected, and transgenic plants frequently display phenotypic features not related to the physiological function of the introduced gene. In this review, we focus on an aspect often neglected in research on plants expressing metal homeostasis genes: the specific regulation of endogenous metal homeostasis genes of the host plant in response to the transgene-induced imbalance of the metal status. These modifications constitute one of the major mechanisms involved in the generation of the plant's phenotype, including unexpected characteristics. Interestingly, activation of so-called “metal cross-homeostasis” has emerged as a factor of primary importance.
Highlights
INTRODUCTIONEngineered metal uptake, organ- and tissue-specific distribution, and tolerance in plants contribute to phytoremediation/phytoextraction (use of plants to remove metals from contaminated soils) and mineral biofortification (optimization of micronutrient contents in plant-derived food and exclusion of toxic metals)
Engineered metal uptake, organ- and tissue-specific distribution, and tolerance in plants contribute to phytoremediation/phytoextraction and mineral biofortification
Plants have been transformed using metal homeostasis genes involved in uptake, compartmentalization, long-distance transport, and chelation of metals
Summary
Engineered metal uptake, organ- and tissue-specific distribution, and tolerance in plants contribute to phytoremediation/phytoextraction (use of plants to remove metals from contaminated soils) and mineral biofortification (optimization of micronutrient contents in plant-derived food and exclusion of toxic metals) For both it is crucial to modify the metal concentration in plant parts (Palmgren et al, 2008; Verbruggen et al, 2009). The development of unexpected features is a manifestation of changes in a range of host-plant endogenous molecular and physiological pathways due to expression of the introduced gene/genes As these alterations substantially contribute to generation of the plant’s phenotype, understanding the underlying mechanisms is crucial for better planning of future modifications of metal accumulation and tolerance, and for Environmental Risk Assessment of genetically modified plants.
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