Comparison of low water potential (drought)-regulated gene expression in wild type (Col-0) and the hai1-2 (At5g59220) mutant. Arabidopsis thaliana

The Clade A PP2C Highly ABA-Induced1 (HAI1, At5g59220) is strongly up-regulated by low water potential in an ABA-dependent manner. Using knockout mutants of hai1, we found that HAI1 functions as a negative regulator of low water potential-induced proline and osmoregulatory solute accumulation. We also found a relatively weak and limited interaction of HAI1 with the RCAR/PYL family of ABA receptors. This, plus its induced expression, suggest that HAI1 remains active during stress and attenuates specific aspects of drought response. Microarray experiments were used to identify genes differentially expressed in hai1-2 (SALK_108282) versus wild type under both unstress control conditions and after low water potential (i.e., drought, water deficit). A relatively long term (96 h) low water potential treatment was used as phenotypes of hai1-2 were most apparent after this longer term low water potential treatment. Overall design: Seven-day-old seedlings of wild type (Col-0) or hai1-2 were transferred from agar plates of control media to low water potential stress (PEG-infused agar plates at -1.2 MPa) or to fresh control media (-0.25 Mpa). Samples (whole seedlings) were collected 96 h after transfer. Three independent experiments were conducted with one sample of each treatment (wild type stress and control, hai1-2 stress and control) collected from each experiment.