Mutant plants that are deficient in brassinosteroid that are grown in the dark, show features of plants grown in the light. They also have defects at many phases of the plant life cycle, including reduced seed germination, dwarfism, and sterility.
The physiological effects of brassinosteroids are very similar to those of gibberellin, another hormone. But the relationship between these two hormones has been unclear at the molecular level. Recent studies of Wang and his colleagues have elucidated the molecular pathway through which brassinosteroid alters gene expression and explored the relationship of the two hormones.
In the two Nature Cell Biology papers, Wang and his team identified key junctions between the molecular pathway that transduces the brassinosteroid signal and those for the light, temperature, and gibberellin signals. The studies explain how multiple environmental and hormonal signals regulate plant growth and development. The studies also elucidate a biochemical "command system" that integrates a wide range of signals into growth regulation.
In contrast to the widely held concept that environmental signals affect endogenous hormones to alter plant growth, the study by Wang found surprisingly that light does not affect brassinosteroid. Instead, brassinosteroid has major effects on the sensitivity of plants to light by not only altering the levels of proteins mediating light responses, but also providing an essential partner for a transcription factor, named PIF4, that is directly inactivated by the photoreceptor phytochrome. The brassinosteroid-activated BZR1 protein and dark-stabilized PIF4 protein form a complex that drives expression of genes required for the etiolation process.
By contrast, light removal of PIF4, or the absence of BZR1 caused by brassinosteroid deficiency, leads to de-etiolation and inhibi
|Contact: Zhiyong Wang |