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Title: Lifting DELLA repression of Arabidopsis seed germination by nonproteolytic gibberellin signaling

item ARIIZUMI, TOHRU - University Of Tsukuba
item HAUVERMALE, AMBER - Washington State University
item NELSON, SVEN - Washington State University
item HANADA, ATSUSHI - Riken Institute
item YAMAGUCHI, SHINJIRO - Riken Institute
item Steber, Camille

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2013
Publication Date: 7/1/2013
Citation: Ariizumi, T., Hauvermale, A.L., Nelson, S.K., Hanada, A., Yamaguchi, S., Steber, C.M. 2013. Lifting DELLA repression of Arabidopsis seed germination by nonproteolytic gibberellin signaling. Plant Physiology. 162(4):2125-39. doi: 10.1104/pp.113.219451.

Interpretive Summary: This paper examines how the GA hormone receptor GID1 (GA-insensitive dwarf 1) functions to stimulate seed after-ripening and germination. Seeds are an important source of human nutrition and a vehicle for plant propogation and dispersal. Making the decision to germinate at the appropriate time is essential both to agriculture and to species survival. Seeds can be dormant when they are first released from the mother plant such that they fail to germinate under favorable conditions. Dormant seeds eventually acquire the ability to germinate through a period of dry storage called after-ripening, and/or through a period of moist chilling called cold stratification.Evidence is presented that GID1 is needed for after-ripening. Overproduction of GID1 also stimulates seed germination without destruction of DELLA inhibitors of seed germination. Thus, GID1 is an important gene for the control of seed dormancy, after-ripening, and germination.

Technical Abstract: DELLA repression of Arabidopsis seed germination can be lifted through the ubiquitin-proteasome pathway and proteolysis-independent GA signaling. GA-binding to the GID1 (GIBBERELLIN-INSENSITIVE DWARF1) GA receptors stimulates GID1-GA-DELLA complex formation which in turn triggers DELLA protein ubiquitination and destruction via the SCFSLY1 E3 ubiqutin ligase and 26S proteasome. The sly1-2 allele results in strong seed dormancy that can be lifted without DELLA proteolysis by long after-ripening or GID1 overexpression (GID1-OE). Dormant sly1-2 seeds accumulate high levels of GA and ABA hormone. ABA signaling is involved in sly1-2 dormancy since abi1-1 (ABA-insensitive1) rescues seed germination, while rescue of sly1-2 germination by after-ripening and GID1b-OE are associated with decreased ABA accumulation. DELLA positively regulates the transcription of XERICO, an inducer of ABA biosynthesis; and sly1-2 results in high level DELLA protein and XERICO mRNA accumulation. Both after-ripening and GID1b-OE result in decreased XERICO mRNA levels without decreasing DELLA protein levels. After-ripening results in increased GA accumulation and signaling and requires GID1a. Rescue of sly1 germination is associated with increased GID1-GA-DELLA complex formation. Thus, with GID1-OE and after-ripening, elevated GID1 protein and GA hormone levels appear to block DELLA activation of the XERICO inhibitor of seed germination through GID1-GA-DELLA protein complex formation.