PERK4 regulates the expression of genes related to cell wall loosening. Total RNA was isolated from the 8-d-old mutant and wild-type seedling roots with or without 100 µM ABA treatment with the TRIzolR reagent (Invitrogen, Carlsbad, CA, USA). qRT-PCR was performed on a Rotor-Gene 3000 (Corbett Research, Australia). Reaction contained 10 µL SYBR Premix Ex Taq (TaKaRa), 0.6 µL primer (to 0.3 µM), 2 µL cDNA, and 6.8 µL deionized water to make a total volume of 20 µL. The gene-specific primers were 5′-TAG CCT CAC CAG CCA CCT CAC TC-3′ and 5′-GCA ATT CCA TAT TCA TCC CAA CC-3′ for the polygalacturonases gene (At3g06770, A), 5′-CCG CAA ATT ACT TCT ACT CTT CC-3′ and 5′-GTA TTC GTA GTG CTT CTT GGG TG-3′ for AtExt1 (B). Actin2 gene was used as a standard control. For relative quantification the method of Pfaffl (2001)27 was used to determine the relative expression ratio. Means ± SD are shown.