UC San Diego

The phytohormone abscisic acid (ABA) plays several critical roles in plant development when induced by abiotic stresses such as drought, salinity, heavy metals, and extreme temperatures. Some of these responses include stomatal closure, inhibition of seed germination, and regulation of root growth, and these responses likely occur due to interactions between ABA and other plant hormones. The crosstalk networks between ABA and other plant hormones are not yet fully understood although several studies have been underway in order to understand the mechanisms by which several signaling pathways respond to abiotic stresses. We have studied a recently discovered involvement of a PYR/PYL ABA receptor, PYL6, and a basic- helix-loop-helix (bHLH) transcription factor (TF), MYC2, in ABA and jasmonic acid (JA) signaling. In order to gain insight on the developmental and spatial expression of PYL6, the [beta]-glucuronidase (GUS) reporter system was utilized to analyze the activity of the promoter and full length gene of PYL6 in plant tissue. GUS expression was detected in the anther of adult transgenic pyl6 mutant plants but not in wild type background plants. Protein- protein-interaction analyses were performed to characterize a potential structural basis of interaction between PYL6 and MYC2. It was seen that several amino acid point mutations in the PYL6 protein sequence have the potential to establish a constitutive interaction between PYL6 and MYC2 with and without enhancement by ABA. Phenotypical assays with two different pyl6 T-DNA insertion mutants displayed ABA and JA hypersensitivity during germination and cotyledon greening but no significantly altered response during root growth