Disease relevance of SIZ1

• Mutant siz1 plants exhibit constitutive systemic-acquired resistance (SAR) characterized by elevated accumulation of salicylic acid (SA), increased expression of pathogenesis-related (PR) genes, and increased resistance to the bacterial pathogen Pseudomonas syringae pv. tomato (Pst) DC3000 [1].

High impact information on SIZ1

• Siz1 is required for SUMO attachment to the S. cerevisiae septins in vivo and strongly stimulates septin sumoylation in vitro [2].
• Siz1 and the related protein Siz2 promote SUMO conjugation to different substrates at different stages of the cell cycle and, together, are required for most SUMO conjugation in yeast [2].
• Lastly, we demonstrate that selection of proper DNA repair pathways to stalled DNA replication forks is controlled by the Mec1-dependent checkpoint and is executed by cooperative functions of Siz1 and Srs2 [3].
• However, yeast mutants lacking the SUMO ligases Siz1 and Siz2/Nfi1 are viable, even though they show dramatically reduced levels of SUMO conjugation [4].
• Most informatively, mutants lacking the SUMO E3 ligase Siz1 are strongly doxorubicin resistant, whereas mutants of other SUMO ligases are either weakly resistant (siz2) or hypersensitive (mms21) to doxorubicin [5].

Biological context of SIZ1

• We propose that SMT4, SIZ1, and SIZ2 are involved in a novel pathway of chromosome maintenance [6].
• SIZ1 interacts epistatically with PAD4 to regulate PR expression and disease resistance [1].
• Taken together, these results demonstrate that SIZ1 is required for SA and PAD4-mediated R gene signalling, which in turn confers innate immunity in Arabidopsis [1].
• Furthermore, Siz1 was localized at the mother-bud neck in the M-phase and physically bound to both E2 and the target proteins [7].
• Transfer of the NahG gene to siz1 plants results in reversal of these phenotypes back to wild-type [1].

Associations of SIZ1 with chemical compounds

• These results suggest that doxorubicin cytotoxicity is regulated by Siz1-dependent sumoylation of specific proteins [5].
• Salicylic acid-mediated innate immunity in Arabidopsis is regulated by SIZ1 SUMO E3 ligase [1].
• Jasmonic acid (JA)-induced PDF1.2 expression and susceptibility to Botrytis cinerea were unaltered in siz1 plants [1].

Other interactions of SIZ1

• The previously uncharacterized SIZ1 (SAP and Miz) gene, which encodes a protein containing a predicted DNA-binding SAP module and a Miz finger, is identified as a bypass suppressor of the growth defect associated with the SMT4 disruption [6].
• Recently, Ull1/Siz1 was discovered as a novel PIAS-type E3 required for septin sumoylation in yeast [8].
• Siz1 is a member of a new family (Miz1, PIAS3, etc.) containing a conserved domain with a similarity to a zinc-binding RING-domain, often found in ubiquitin ligases [7].

References