Plants defense responses can be triggered by endogenous elicitors, which are released upon pathogen infection or mechanical injury, indicated as damage-associated molecular patterns (DAMPs). Among DAMPs, there are fragments originating from cell wall polysaccharides, such as the oligogalacturonides (OGs). The activity of OGs as DAMPs is well documented(Ferrari et al. 2013). Benedetti et al. 2018 have recently identified a possible mechanism by which the homeostasis of OGs may be maintained by specific oxidases named OGOXs. These enzymes belong to the so-called berberine-bridge enzyme-like (BBEl) family. A role of OGOXs in immunity has been demonstrated. Besides OGs, other oligosaccharides released from the cell wall have been recently shown to be involved in signaling, for example, cellodextrins (CDs) derived from the degradation of cellulose have been shown to act as DAMPs. In the laboratory where I perform my thesis, one member of the Arabidopsis BBEl family has been recently identified as a specific oxidase of CDs: CELLOX1. The aim of my project is to characterize part of the BBE-like family oxidases and to identify their substrates and the respective products. In general my research will address the problem of controlling immunity triggered by DAMPs and preventing their deleterious effects. Whether cell wall-derived DAMPs act in concert and their oxidation merely dampens the immune response or modulates it for a finely tuned output will be defined. Moreover, my work may elucidate the role of cell-wall derived signals in development. This knowledge may be exploited to improve resistance of crops to biotic stresses, and to optimize plant development and growth.
This is a novel research area that will address the control of immunity triggered by cell wall-derived DAMPs to prevent deleterious effects in plants. Whether cell wall-derived DAMPs act in concert and their oxidation merely dampens the immune response or modulates it for a finely tuned output will be defined.
The research group to which I belong has recently identified a possible mechanism by which the homeostasis of DAMPS such as oligogalacturonides (OGs) activity may be maintained, represented by specific oxidases named OGOX that inactivate OGs. These enzymes belong to the so-called berberine-bridge enzyme-like (BBEl) family (Benedetti et al. 2018). At least four members of this family, which comprises a total of 27 members, are OG oxidases (OGOX1, OGOX2, OGOX3, and OGOX4); an additional fifth member to characterize in this project may also be an OGOX.
Notably, in the laboratory where I perform my thesis, one member of the Arabidopsis BBEl family has been recently identified as a specific oxidase of cellodextrins and has been therefore named CELLOX1, and a paralogue of this enzyme is also going to be studied.
Interestingly, the oxidation of OGs, and cellodextrins is accompanied by the formation of H2O2. H2O2 has plays an important role in defense, directly by participating as cell wall strengthening factor (cross-linking of structural protein and lignin polymers) or giving cytotoxic effect against pathogens, or indirectly, acting as a second messenger in signaling and in wound repair, for example at the sites of cell-wall ruptures and micro-lesions during plant growth and development (Levine et al. 1994, Galletti et al. 2008, Benedetti et al. 2018). The significance of OGOX/CELLOX-mediated H2O2 production has to be elucidated.
H2O2 could have a function in signaling in the defense response, or might be a substrate for the lignin-forming peroxidases. It has been shown that the level of resistance to the infection raises with the increasing oxidase expression level (Custers et al. 2004). The same hypothesis may apply to OGOXs and CELLOXs.
Moreover, the work may elucidate the role of cell-wall derived signals in development, because of the defense-growth trade-off implications, and the involvment of the cell-wall in the plant extension.
Knowledge acquired may be exploited to improve crops resistance to biotic stresses, associated with an optimization of plant development and growth.
Benedetti, M., I. Verrascina, D. Pontiggia, F. Locci, B. Mattei, G. De Lorenzo & F. Cervone (2018). Plant Journal, 94(2), 260-273.
Custers, J. H., S. J. Harrison, M. B. Sela-Buurlage, E. van Deventer, W. Lageweg, P. W. Howe, P. J. van der Meijs, A. S. Ponstein, B. H. Simons, L. S. Melchers & M. H. Stuiver (2004). Plant J, 39, 147-60.
Galletti, R., C. Denoux, S. Gambetta, J. Dewdney, F. M. Ausubel, G. De Lorenzo & S. Ferrari (2008). Plant Physiology, 148, 1695-1706.
Levine, A., R. Tenhaken, R. Dixon & C. Lamb (1994). Cell, 79, 583-593.