Wheat cysteine proteases triticain α, β and γ exhibit mutually distinct responses to gibberellin in germinating seeds

We cloned three novel papain-type cysteine proteases (CPs), triticain α, β and γ, from 1-d-germinating wheat seeds. Triticain α, β and γ were constituted with 461, 472 and 365 amino acid residues, respectively, and had Cys–His–Asn catalytic triads as well as signal and propeptide sequences. Triticain γ contained a putative vacuole-sorting sequence. Phylogenetic analysis showed that these CPs were divided into mutually different clusters. Triticain α and γ mRNAs were expressed in seeds at an early stage of maturation and at the stage of germination 2 d after imbibition, while triticain β mRNA appeared shortly after imbibition. The expression of mRNAs for triticain α and γ was suppressed by uniconazol, a gibberellin synthesis inhibitor. All the three CP mRNAs were strongly expressed in both embryo and aleurone layers. These results suggest that triticain α, β and γ play differential roles in seed maturation as well as in digestion of storage proteins during germination.