Gibberellin signaling expands to include the UBX domain protein PUX1, a new binding partner for GID1

Authors: HAUVERMALE, AMBER - Washington State University; CARDENAS, JESSICA - Washington State University; BEDNAREK, SEBASTIAN - Washington State University; Steber, Camille

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/19/2022
Publication Date: 9/23/2022
Citation: Hauvermale, A., Cardenas, J.J., Bednarek, S.Y., Steber, C.M. 2022. Gibberellin signaling expands to include the UBX domain protein PUX1, a new binding partner for GID1. Plant Physiology. 190(4):2651-2670. https://doi.org/10.1093/plphys/kiac406.
DOI: https://doi.org/10.1093/plphys/kiac406

Interpretive Summary: Gibberellins (GAs) are plant hormones that stimulate seed germination, the transition to flowering, and cell elongation and division. The GA signal is perceived by a receptor call GID1 (GA-insensitive dwarf1). Previous work showed the GID1 stimulates germination, flowering, stem elongation, and fertility by interaction with and destruction of DELLA repressors of GA response. This study identified a new GID1-interacting protein, the plant UBX-domain protein PUX1. Mutations in PUX1 result in a "GA overdose" effect in Arabidopsis plants including earlier flowering, taller plants, and seeds with better germination. PUX1 may represent a new way to modify these GA-regulated processes in crop plants.

Technical Abstract: The plant UBX-domain containing protein, PUX1, functions as a negative regulator of gibberellin signaling. Gibberellins (GAs) are plant hormones that stimulate seed germination, the transition to flowering, and cell elongation and division. Loss of PUX1 resulted in a “GA-overdose” phenotype including early flowering, increased stem and root elongation, and partial resistance to the GA-biosynthesis inhibitor paclobutrazol during seed germination and root elongation. Furthermore, GA application failed to stimulate further stem elongation or flowering onset suggesting that elongation and flowering response to GA had reached its maximum. GA hormone partially repressed PUX1 protein accumulation, and PUX1 showed a GA-independent interaction with the GA receptor GID1. This suggests that PUX1 is GA regulated and/or regulates elements of the GA signaling pathway. Consistent with PUX1 function as a negative regulator of GA signaling, the pux1 mutant caused increased GID1 expression and decreased accumulation of the DELLA RGA repressor of GA responses. PUX1 is a negative regulator of the hexameric AAA-ATPase CDC48, a protein that functions in diverse cellular processes including unfolding proteins in preparation for proteasomal degradation, cell division and expansion. PUX1 binding to GID1 required the UBX domain, a binding motif necessary for CDC48 interaction. Moreover, PUX1 overexpression in cell culture not only stimulated the disassembly of CDC48 hexamer, it also resulted in co-fractionation of GID1, PUX1, and CDC48 subunits in velocity sedimentation assays. Based on our results, we propose that PUX1 and CDC48 are additional factors that need to be incorporated into our understanding of GA signaling.