Generating Yeast One-Hybrid DNA-Bait Strains

The maize aquaporin ZmPIP1;6 enhances stomatal opening and CO2- and ABA-induced stomatal closure

The plasma membrane aquaporin ZmPIP1;6 is expressed in maize stomatal complexes, with higher expression during the day than at night. To elucidate the role of ZmPIP1;6 in gas exchange and stomatal movement, it was expressed in maize (inbred line B104) under the control of p35S promoter (OE) or its native promoter fused with mYFP cDNA (mYFP-ZmPIP1;6). In stomatal complexes of the leaf mature zone, mYFP-ZmPIP1;6 showed higher expression in subsidiary cells than in guard cells, with light and dark treatments influencing its subcellular localization. Notably, ZmPIP1;6 internalization increased in dark conditions versus light. Stomatal opening was greater in ZmPIP1;6 OE than in wild type (WT), while closure exhibited greater sensitivity to elevated CO2 concentration or ABA treatment. Our finding revealed that reactive oxygen species (H2O2) was involved in ABA-induced stomatal closure, while ZmPIP1;6 was unable to facilitate H2O2 diffusion when expressed in yeast. Finally, ZmPIP1;6 OE and mYFP-ZmPIP1;6 transgenic plants exhibited higher abaxial stomatal density than WT. Overall, these results indicate that ZmPIP1;6 plays important roles in stomatal opening and CO2- and ABA-induced stomatal closure.

Identifying Interactors from an Activation Domain Prey Library

In yeast hybrid assays, the process of identifying preys that interact with the bait of interest involves several steps. First, in this protocol, the bait yeast strain is transformed with a library of activation domain (AD)-prey clones and plated on selective media containing 3-aminotriazole (3AT). This selects transformants containing an AD-prey clone that induces HIS3 reporter expression. Second, these "HIS-positive" colonies are analyzed for LacZ induction (and, optionally, URA3 induction in yeast two-hybrid (Y2H) assays). Third, yeast PCR is used on these "double-positive" colonies to amplify the insert from the AD-prey plasmid. Fourth, some of this PCR product is used to perform a gap-repair retest to confirm the interaction in fresh bait-strain yeast, and the remainder is used for DNA sequencing to determine prey identity for those that successfully retest. Finally, interactions are carefully examined to filter out likely false-positive interactions. This protocol takes 20-43 d plus sequence confirmation to complete.

Generating Yeast Two-Hybrid Bait Strains

Generating DNA-binding domain (DB)-bait strains for Gateway-compatible yeast two-hybrid (Y2H) screens involves three steps. The first is to generate an Entry clone containing a DNA fragment encoding the protein of interest (e.g., an open reading frame, ORF). The second is to transfer this DNA fragment from the Entry clone to the Y2H Destination vector, pDEST32. The final step is to transform this construct into the Y2H yeast strain, MaV103. This protocol takes 24-37 d plus sequence confirmation, if necessary, to complete.

Gateway-Compatible Yeast One-Hybrid and Two-Hybrid Assays

In the first section of this introduction, we provide background information for yeast two-hybrid (Y2H) assays that provide a genetic method for the identification and analysis of binary protein-protein interactions and that are complementary to biochemical methods such as immunoprecipitation. In the second section, we discuss yeast one-hybrid (Y1H) assays that provide a "gene-centered" (DNA-to-protein) genetic method to identify and study protein-DNA interactions between cis-regulatory elements and transcription factors (TFs). This method is complementary to "TF-centered" (protein-to-DNA) biochemical methods such as chromatin immunoprecipitation.

High-Efficiency Yeast Transformation

High-efficiency yeast transformation is used for integrations into YM4271 (yeast one-hybrid (Y1H) DNA-bait generation), for transforming libraries of activation domain (AD)-prey clones into Y1H and yeast two-hybrid (Y2H)-bait strains, and for gap repair. The protocol takes 2 d to complete.