Hormonal Regulation of Expression of Two Cysteine Endopeptidase Genes in Rice Seedlings

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Two cDNA probes (pRP60 and pRP80) were used to examine the hormonal regulation of expression of two cys-teine endopeptidase genes in germinated whole seeds and de-embryonated seeds of rice. The pRP60 protein is a major rice cysteine endopeptidase named REP-1 that digests rice glutelin, the main seed storage protein. The pRP80 protein has features of a cysteine endopeptidase but has not yet been confirmed to be one. Neither mRNA was detectable in dry seeds, and the levels per seed increased sharply upon inbibition, reached peaks at d 6 to d 9, and then de-creased. Both mRNAS Were expressed in a seed-specific manner, but the accumulation of pRP60 mRNA was about ten times greater than the other. When seeds were de-embryonated and incubated, the amounts of both mRNAS Were reduced to very low levels, but in the presence of 0.01 to I μM gibberellic acid (GA_3) both again reached high levels. Addition of abscisic acid (ABA) or uniconazole, an inhibitor of gibberellin biosynthesis, partly eliminated the effect of GA_3. Protein immunoblot analysis showed that the accu-mulation of the REP-1 protein in seeds was regulated by GA_3 and ABA similarly to that of pRP60 mRNA, but the change in pRP60 mRNA with time after the onset of imbibition preceded that of the REP-1 protein.
日本植物生理学会の論文