Mechanisms of Heterosis in Crop Plants

Summary Although the biological basis of heterosis remains unknown, plant breeders have made wide use of this phenomenon and it is generally believed that the understanding of the mechanisms underlying heterosis will enhance our ability to form new genotypes which may be used directly as F1 hybrids or form the basis for future selection programmes. The original data concerning the phenomenon came out of studies at the phenotypic level. They were followed by physiological and later by biochemical data with the advent of electrophoresis and the easy accumulation of data related to isozyme variability. More recently, efforts have been made at the molecular level and the results suggest the significance of both the regulatory proteins (and their encoding genes) and the mechanisms of regulation of gene activity in manifestation of complicated phenomena such as heterosis. In this article emphasis is given to the molecular mechanisms of heterosis. Recent data on quantifying gene expression at the protein or mRNA level in different parental inbreds and F1 hybrids, and some regulatory mechanisms involved such as transcription factor protein and genomic DNA methylation are discussed.