Regulation of Auxin Receptor Gene Family by Hormonal and Abiotic Stress
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The plant hormone auxin controls growth and development by regulating the expression of many auxin responsive genes. TIR1/AFBs, a family of F-Box proteins act as receptors for auxin. In response to auxin, a group of transcriptional repressor proteins known as Aux/IAAs are degraded through the ubiquitin-proteasome pathway involving SCFTIR1/AFBs. According to recent studies, adaptive response to abiotic and biotic stresses is partly achieved through auxin signaling. It is also known that plant responses to salinity and osmotic stresses are partly controlled through abscisic acid (ABA) signaling, and ABA synthesis is enhanced in response to stress. Auxin signaling is also modulated by ABA. Therefore, I sought to determine the effect of salinity and osmotic stress on the expression of auxin receptor F-Box genes. Furthermore, I examined the effect of ABA on auxin receptor gene expression. Finally, since gibberellic acid (GA) antagonizes ABA, I tested GA effects on auxin receptor genes. Our data indicate that TIR1 expression is up-regulated in response to mild salinity, osmotic stresses, ABA and GA. Even though TIR1/AFBs are known to have similar functions, each of them is regulated differently by above conditions. The complex regulation of TIR1/AFBs may modulate the auxin response, and thereby adapt the plant to the changing environment. Molecular and physiological data support the hypothesis that modulation of auxin response through the regulation of auxin receptor genes leads to changes in physiological responses that ultimately may help the plant to adjust to adverse environments. Better understanding of molecular mechanisms involved in plant auxin response during environmental stress will enable scientists to develop superior crop plants that can thrive under adverse conditions. Further, understanding plant hormone crosstalk will fill the gaps in plant hormone signaling network.