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Title: The role of mitogen-activated protein kinase signalling to regulate leaf growth in response to environmental signals
Author: Bimal, Sujan
ISNI:       0000 0004 8498 7286
Awarding Body: Royal Holloway, University of London
Current Institution: Royal Holloway, University of London
Date of Award: 2016
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Better understanding how plants growth is in tune with limiting environment is fundamental in efforts to improve stress tolerance. Arabidopsis thaliana provides a model system to study the signalling pathways that transmit signals for stress adaptation. Drought is one of the most prevalent abiotic stress to consider. I have set up a screen for stress induced mitogen-activated protein kinase signalling pathways using inducible overexpression of gain of function MAPK kinases (MKKs). Among the 10 Arabidopsis MKKs I have found two; MKK7 and MKK9 that significantly altered the growth of both roots and shoots including leaves. I have characterised the expression of these MKKs on the protein level, and the induction of two downstream MAPKs, MPK3 and MPK6. I set up experimental conditions that mimick mild drought stress using mannitol that limit leaf growth by 50 percent. Using the estradiol inducible overexpression lines for MKK7 and MKK9, as well as insertional mutant lines of mkk7, mkk9, mpk3 and mpk6 I tested the involvement of these MAPK signalling pathways in transducing drought stress and thereby regulating cell proliferation and leaf growth. I used the mitotic cell cycle marker, CycB1;1-DB-GUS reporter, flow cytometry and cell size imaging through DIC and confocal microscopy in these experiments. In paralell to these drought experiments we found that dark stress also induces the MAPK signalling pathway. To characterise the role of MKK7, MKK9, MPK6 and MPK3 in dark-induced growth arres of leaves, I set up deetiolation experiments and imaged emerging leaves upon transfer to light. I found that MPK6 is involved in the initial leaf growth after dark arrest. This work was later followed up and led to the conclusion that the MAPK pathway may regulate auxin transport. I also set out to investigate whether drought and the MKK7, MKK9 MAPK signalling might regulate cell proliferation through the RETINOBLASTOMA RELATED (RBR) protein and E2F transcription factors. To this end, I showed that drought stress influence RBR phosphorylation and promotes RBR interaction with E2FB. I made crosses with the inducible MKK7 and MKK9 lines and the E2FA-GFP, E2FB-GFP to look for the regulation of RBR-E2FB interaction when these MPK pathways are induced. In summary, my research identified the MKK7 and MKK9 pathways regulate leaf growth and cell proliferation. Modulating these signalling pathways could help to obtain crops that better adapt their growth to limiting environmental conditions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available