REPETITIVE NONCODING DNA A POSSIBLE LINK BETWEEN ENVIRONMENT AND GENE-EXPRESSION IN PLANTS

Many experimental results over the last few years have shown that external environmental stimuli are able to induce quantitative and qualitative modifications in the repetitive/noncoding fraction of nuclear DNA in plants. These variations are, unlike mutations, quantitatively significant, usually (but not always) transitory and clearly non-random in that the same effects seem to consistently accompany determined environmental stimuli. Furthermore recent research has shown that the repetitive/non-coding fraction of the genome can influence, mainly by conformational effects. gene expression itself. In this paper, observing in plants the two different types of phenomena in parallel, the author hypothesizes that repetitive/non-coding DNA sequences may, in addition to other functions, act as mediators between the environment and gene expression: in other words, the non-coding sequences of DNA might be able to receive messages from the environment, modify themselves accordingly, and hence influence, in conformity with these messages, the expression or non-expression of specific sets of genes. In this way an equilibrium would be created between the genotype and the environment, an equilibrium which could be altered during particular pathological situations. Current data in the literature concerning plants are analyzed and discussed in the context of this hypothesis.