SMALL ACIDIC PROTEIN1 Acts with RUB Modification Components, the COP9 Signalosome, and AXR1 to Regulate Growth and Development of Arabidopsis      

Abstract

Previously, a dysfunction of the SMALL ACIDIC PROTEIN1 (SMAP1) gene was identified as the cause of the anti-auxin resistant1 (aar1) mutant of Arabidopsis (Arabidopsis thaliana). SMAP1 is involved in the response pathway of synthetic auxin, 2,4-dichlorophenoxyacetic acid, and functions upstream of the auxin/indole-3-acetic acid protein degradation step in auxin signaling. However, the exact mechanism by which SMAP1 functions in auxin signaling remains unknown. Here, we demonstrate that SMAP1 is required for normal plant growth and development and the root response to indole-3-acetic acid or methyl jasmonate in the auxin resistant1 (axr1) mutation background. Deletion analysis and green fluorescent protein/ glutathione S-transferase pull-down assays showed that SMAP1 physically interacts with the CONSTITUTIVE PHOTOMORPHOGENIC9 SIGNALOSOME (CSN) via the SMAP1 F/D region. The extremely dwarf phenotype of the aar1-1 csn5a-1 double mutant confirms the functional role of SMAP1 in plant growth and development under limiting CSN functionality. Our findings suggest that SMAP1 is involved in the auxin response and possibly in other cullin-RING ubiquitin ligase-regulated signaling processes via its interaction with components associated with RELATED TO UBIQUITIN modification.

Myeloma Overexpressed 2 (Myeov2) Regulates L11 Subnuclear Localization through Nedd8 Modification

“…Intriguingly, plant Myeov2 homolog, Smap1 and Smap2, have genetic and physical interactions with a subset of COP9 subunits. An ectopic expression of Smap1 partially compensated the morphological defect of CSN5a mutant in plants, although Smap1 does not deconjugate Nedd8 from Cul1 [38], [39], [40]. This observation is consistent with our data that expression of Myeov2 did not enhance the activity of COP9 signalosome, despite of its interaction (Fig.…”

The NEDD8 modification pathway in plants

“…The 7 kDa protein SMALL ACIDIC PROTEIN1 (SMAP1) is an interesting CSN-interaction partner (Nakasone et al, 2012). smap1 mutants were identified as anti-auxin resistant1 ( aar1 ) in a mutant screen that also identified mutants of TIR1 , CULLIN1 , and DCN1-LIKE .…”

Lack of SMALL ACIDIC PROTEIN 1 (SMAP1) causes increased sensitivity to an inhibitor of RUB/NEDD8-activating enzyme inArabidopsisseedlings

“…This evidence indicates a close functional relationship between SMAP1 and AXR1. 6 A similar genetic interaction was observed for AXR1-LIKE (AXL), a homolog of the AXR1; although axl mutants resemble wild-type (WT) plants, axr1 axl double mutants fail to establish root meristems and subsequently die. 8 AXR1 and AXL encode subunits of RUB-activating E1 enzyme, promote posttranslational RUB modification, and regulate CRL activity.…”

“…1 SMAP1 physically binds the evolutionarily conserved CONSTITUTIVE PHOTOMORPHOGENIC-9 SIGNALOSOME (CSN) complex, through the SMAP1 F/D-region. 6 CSN has metalloprotease activity, via its CSN5 subunit, and de-conjugates RUB/ NEDD8 from CULs. 7 Genetic evidence indicates that SMAP1 functions with AUXIN RESISTANT 1 (AXR1).…”

“…7 Genetic evidence indicates that SMAP1 functions with AUXIN RESISTANT 1 (AXR1). 6 The aar1 mutants have longer hypocotyls and petioles in young seedlings. 4 However, the axr1 aar1 double mutants exhibit severe morphological defects, including failure of root meristem formation.…”