Trichomes of Higher Plants: Homologous Series in Hereditary Variability and Molecular Genetic Mechanisms

The diversity of trichomes is extremely large in the plant kingdom: this is the pubescence of leaves and glumes in cereals and fruits and petioles in fruit plants, thorns in rose and cucumber, hairs on Drosera leaves, or cotton fibers. Trichomes vary in shape, size, structure, location, capability to secrete, etc. All trichomes share a common basic function—protecting plants from various biotic and abiotic factors. Artificial selection sometimes works against the development of trichomes. For example, in the selection of fruit trees, preference is given to those with smooth fruits. Among wild species, intraspecific variability on the presence/absence of trichomes was also detected. The aim of this review is to compare the mechanisms of formation of trichomes in different species in order to estimate extension of homologous series in hereditary variability within different taxa. Data on the morphology of trichomes are summarized. Data on genes determining variability are compared, and orthologous genes are revealed. Comparison with data on gene networks involved in the development of trichomes indicates that, despite the common molecular mechanisms of trichome development in all higher plants, mutations of different components of this gene network confer observed variability within different taxa.