Members of the Universal Stress Protein Family are Indirectly Involved in Gibberellin-Dependent Regulation of Germination and Post-Germination Growth

Functional activity of the studied members of the universal stress protein (USP) family is primarily considered in the context of resistance to various stress factors. Also, USP proteins are involved in the regulation of plant growth and development and may act alone or in association with interacting partners. Our study demonstrates the involvement of GRUSP protein (Germination–Related USP; AT3G58450) in gibberellin-dependent germination. In Arabidopsis thaliana (L.) Heynh grusp-115 mutant line, suppression of At3g58450 expression led to an altered response to exogenous gibberellins (GA), demonstrating a reduced sensitivity to GA comparing with Col-0. Simultaneously, the inhibitory effect of paclobutrazol, an inhibitor of GA biosynthesis, was more pronounced in grusp-115, which is a consequence of the altered initial transcript level of some genes encoding enzymes of GA metabolism. Moreover, dysfunction of GRUSP delayed development of grusp-115 seedlings might be a result of an increased initial level of GAI, acting as a repressor of GA signaling, with subsequent slower degradation during seed germination. Our data indicate the involvement of GRUSP in GA-dependent regulation of seed germination and post-emergence growth, probably indirectly and potentially involving other members of the USP family, AT3G11930 and AT2G47710, in this process.