The molecular mechanisms regulating hormone synthesis,
signaling, and action have been elucidated during the past
few years, and the roles of plant hormones for responses to
changing environments have been demonstrated. These
findings will facilitate the modification of hormone biosynthetic
pathways for the generation of transgenic plants with
enhanced abiotic stress tolerance. Controlling the hormone
dose/response ratio remains a challenge, since the hormone
levels attained should be moderate in order to maintain a
balance between the positive effects of plant hormones on
stress tolerance and the negative effects on growth and
development. The use of conditional promoters driving
gene expression at specific developmental stages, in
specific tissues/organs and/or in response to specific
environmental cues circumvents this problem and will
facilitate the generation of transgenic crops able to grow
under various abiotic stresses with minimal yield losses.