Programmed cell death (PCD) is an active process by which organisms
coordinate the controlled destruction of cells. In tomato, the protein kinase Adi3
(AvrPto-dependent Pto-interacting kinase 3), acts as a negative regulator of PCD and shares important functional homologies with the mammalian anti-apoptotic AGC kinase
PBK/Akt. Adi3 was originally identified as an interactor of the complex formed by the
tomato resistance protein Pto and the Pseudomonas syringae pv. tomato (Pst) effector
protein AvrPto. The complex formed by AvrPto and Pto causes a resistance response
characterized by a rapid form of PCD that limits the spread of Pst and prevents the onset
of the tomato bacterial speck disease.
In an effort to characterize the mechanisms by which Adi3 regulates PCD, we identified Adi3 interacting partners in a Y2H screen. Here, I describe the interaction of
Adi3 with two interacting partners identified: the Sucrose Non-fermenting (SNF1)
kinase complex (SnRK) which is a eukaryotic master regulator of energy homeostasis
and the E3 RING Ubiquitin ligase AdBiL.
Using a combination of in vitro and in vivo approaches I found that AdBiL is an active ubiquitin ligase that ubiquitinates Adi3. Interestingly, Adi3 was found to be
degraded in a proteasome-dependent manner suggesting ubiquitination could play a role in its degradation. On the other hand, Adi3 was found to inhibit the SnRK complex by directly interacting with its catalytic subunit as well as by phosphorylating the regulatory subunit SlGal83 at Ser26. SlGal83 is phosphorylated at multiple sites in vivo, and this phosphorylation state, as well as its intracellular localization was found to depend on a myristoylation signal present at its N-terminus. Phosphorylation at Ser26 by Adi3 was found to alter the localization of this subunit in a myristoylation-dependent manner.
The interactions studied in this dissertation provide additional evidence on the functional homologies shared by Adi3 and PKB. In addition, the regulatory control of SnRK activity and cellular localization offers a novel connection between pathways
involved in energy homeostasis and pathogen-mediated PCD.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/148132 |
| Date | 14 March 2013 |
| Creators | Avila Pacheco, Julian Ricardo, 1983- |
| Contributors | Devarenne, Timothy P, Kolomiets, Mikhailo, Straight, Paul, Pellois, Jean-Philippe |
| Source Sets | Texas A and M University |
| Detected Language | English |
| Type | Thesis, text |
| Format | application/pdf |
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