Peptide transporter2 (PTR2) enhances water uptake during early seed germination in Arabidopsis thaliana

Abstract

Key messagePTR2 inArabidopsis thalianais negatively regulated by ABI4 and plays a key role in water uptake by seeds, ensuring that imbibed seeds proceed to germination.AbstractPeptide transporters (PTRs) transport nitrogen-containing substrates in a proton-dependent manner. Among the six PTRs inArabidopsis thaliana, the physiological role of the tonoplast-localized, seed embryo abundant PTR2 is unknown. In the present study, a molecular physiological analysis of PTR2 was conducted usingptr2mutants andPTR2COcomplementation lines. Compared with the wild type, theptr2mutant showed ca. 6 h delay in testa rupture and consequently endosperm rupture because of 17% lower water content and 10% higher free abscisic acid (ABA) content. Constitutive overexpression of thePTR2gene under the control of the Cauliflower mosaic virus (CaMV)35Spromoter inptr2mutants rescued the mutant phenotypes. After cold stratification, a transient increase inABA INSENSITIVE4(ABI4) transcript levels during induction of testa rupture was followed by a similar increase inPTR2transcript levels, which peaked prior to endosperm rupture. ThePTR2promoter region containing multiple CCAC motifs was recognized by ABI4 in electrophoretic mobility shift assays, andPTR2expression was repressed by 67% inABI4overexpression lines compared with the wild type, suggesting that PTR2 is an immediate downstream target of ABI4. Taken together, the results suggest that ABI4-dependent temporal regulation ofPTR2expression may influence water status during seed germination to promote the post-germinative growth of imbibed seeds.