Page 249 - PC2019 Program & Proceedings

PLANT CANADA 2019

P71. Using interactome and ubiquitinome datasets to identify substrates for Arabidopsis RING-
type ubiquitin ligases (E3s) and the ubiquitin system
Alotaibi, D.; J. Yang; L. Hongxia; Stone, S.
Dalhousie University

Ubiquitination involves the attachment of ubiquitin, a small ubiquitous protein, to a substrate leading to
different outcomes. For example, attachment of one ubiquitin may influence localization, while a
polyubiquitin chain may result in degradation by the proteasome. E3s facilitate ubiquitin conjugation,
govern substrate protein selection, and are involved many processes including stress responses,
growth and development. However, lack of substrate identity prevents a comprehensive understanding of
E3 function. Utilizing interactome datasets we found 1484 interactions for 200 RING-type E3s
representing 830 potential interactors. Survey of selected publications found 3768 ubiquitinated proteins,
and 144 are among the identified interactors. Using in vivo degradation and interaction assays we
demonstrate that interactors, such as CIPKs, are bona fide substrates. ESCRT III (not I and
II) components and 10 of 24 TCP transcription factors are among the interactors. Other transcription
factor families, e.g. MYB and NAC, were less represented among both datasets. MAPKs were mainly
associated with SINAT E3s, many of which are ubiquitinated. 250 interactions were found for the ATL
E3s including 14-3-3 proteins (14‐3‐3χ is an ATL31 interactor), which are amongst proteins found most
frequently within ubiquitinome datasets. Many interactors are associated with multiple E3s and vice
versa. The membrane-localized pathogen-responsive NHL3 is ubiquitinated and associates with over 20
membrane-localized (predicted) E3s. COP1 has the majority of potential interactors (>50). Although
limited, the available data sheds light on potential substrates for the RING-type E3s and ubiquitin system.

Sophia Stone (sophia.stone@dal.ca)

P72. Transcriptional control of bacterial cell division in a nitrogen fixing symbiosis
D'Alessio, M.; J. Cheng; A. Doxey; Charles, T.
University of Waterloo

The Sinorhizobium meliloti ExoR/ExoS/ChvI transcriptional regulatory system controls a large number of
genes, several of which are directly or indirectly involved in symbiosis with alfalfa. Disruption or
inactivation results in root nodules that do not fully develop, and nitrogen fixation does not occur. Other
associated phenotypes include inability to grow on complex media, sensitivity to acidic pH and
detergents, decreased production of PHB, and altered motility and carbon source utilization. Previous
work identified a number of genes that are directly bound by ChvI transcriptional regulator, and resulted
in the discovery of a binding site motif. To further investigate the regulatory circuitry, we performed
transcriptome analysis using RNA-seq. This led to the prediction of an influence on the expression of cell
cycle regulation genes, and a prominently localized effect proximal to the origin of replication of pSymA,
the symbiotic megaplasmid. We propose that this transcriptional regulatory system, through control of the
activity of the master cell cycle synchronization protein CtrA, is required for full transition of the
invading bacterial cell to the nitrogen fixing symbiosis state.

Trevor Charles (tcharles@uwaterloo.ca)

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