Possible roles of basic helix-loop-helix transcription factors in adaptation to drought.

Water deficiency decreases plant growth and productivity. Several mechanisms are activated in response to dehydration that allows plants to cope with stress, including factors controlling stomatal aperture and ramified root system development. In addition, ABA metabolism is also implicated in the regulation of drought responses. The basic helix-loop-helix (bHLH) proteins, a large family of conserved transcription factors that regulates many cellular processes in eukaryotic organisms, are also involved in several responses that are important for plants to cope with drought stress. This review discusses distinct mechanisms related to drought-adaptive responses, especially the possible involvement of the bHLH transcription factors such as MUTE, implicated in stomatal development; RD22, [corrected] an ABA-responsive gene; EGL3 and GL3, involved in thichome and root hair development; and SPT, which play roles in repressing leaf expansion. Transcription factors are potential targets for new strategies to increase the tolerance of cultivars to drought stress. Recognition of gene regulatory networks in crops is challenging, and the manipulation of bHLH genes as well as components that mediate bHLH transcription factor responses in different pathways could be essential to achieve abiotic stress tolerance in plants through genetic manipulation.