The 26S proteasome of the resurrection plant Tortula ruralis: Cloning and characterization of the TrRPT2 subunit

Abstract

Tortula ruralis is an important experimental system for the study of plant desiccation tolerance. EST gene discovery efforts utilizing desiccated gametophytes have identified a cDNA TrRpt2 encoding a predicted polypeptide with significant similarity to the 26S proteasome regulatory subunit IV. TrRPT2, the 446 amino acid deduced polypeptide, has a predicted molecular mass of 49.6 kDa, and a predicted pI of 8.15. Phylogenetic analysis demonstrated that previously characterized RPT2 polypeptide sequences could be reproducibly grouped into 3 major clades and that TrRPT2 forms a discrete evolutionary group. RNA blot hybridizations were used to analyze TrRpt2 expression in response to: 1) desiccation and rehydration, 2) abscisic acid-treatment, 3) increased NaCl concentration, and 4) NaCl-shock. TrRpt2 steady-state mRNA transcript levels are unchanged in response to all treatments and the gene is constitutively expressed.