Mahmood, Kashif - University of Guelph

ANNOUNCEMENT:
Interested members of the University
Community are invited to attend the
Final Oral Examination for the Degree
of Doctor of Philosophy of
Kashif Mahmood
of the Department of Molecular and Cellular Biology
on Wednesday, December 17, 2014 at 1:00 p.m. in SCIE 1511
Thesis Title:
ARABIDOPSIS NAC TRANSCRIPTION FACTORS:
ROLES IN NATURAL AND STRESS-INDUCED SENESCENCE
Examination Committee:
Dr. A. Bendall, Dept. of Molecular and Cellular Biology (Chair)
Dr. J. Colasanti, Dept. of Molecular and Cellular Biology
Dr. D. Wolyn, Dept. of Plant Agriculture
Dr. A. Nassuth, Dept. of Molecular and Cellular Biology
Dr. R. Cameron, Dept. of Biology, McMaster University
ABSTRACT
Kashif Mahmmod, B.Sc., M.Phil.
Advisor: Dr. S. Rothstein
Plant senescence is an important biological phenomenon that involves systematic degradation of plant
cells and tissue structures. Whereas, this process is important for the efficient remobilization of nutrients
from old tissues to newly developing sinks, induction of premature senescence in response to abiotic and
biotic stresses is responsible for immense yield losses in crop plants worldwide. Investigating this
process, therefore, holds a great promise in improving yield potential and nutritional quality under
optimal and stress conditions. Plants respond to internal and external stimuli through the modulation of
gene expression. Several members of the NAC [for NAM (no apical meristem), ATAF, CUC (cup-shaped
cotyledon)] transcription factor family are differentially expressed during developmental as well as during
environmentally-induced senescence in Arabidopsis thaliana. The main objective of this thesis was to
investigate the roles of three such senescence induced members in Arabidopsis thaliana, ANAC032,
ANAC046 and ANAC087, during natural senescence and under different stress conditions. The study
involved the use of different transgenic approaches combined with molecular and biochemical analyses to
determine the physiological functions of these transcription factors. The results showed that ANAC032
positively regulates natural and dark-induced leaf senescence. Detailed analyses of ANAC032 transgenic
plants further showed that ANAC032 has a senescence promoting role in response to oxidative stressinducing conditions as well as during osmotic and salinity stresses. ANAC046 and ANA087 were not
found to be important during natural leaf senescence. The detailed characterization of ANAC046 and
ANAC087 transgenic lines in response to different oxidative stress-inducing conditions showed that
ANAC046 positively regulates senescence in response to oxidative stresses imposed by 3-aminotriazole
(3-AT) and paraquat treatment. In contrast, ANAC087 was only found to negatively regulate responses to
fumonisin B1 (FB1), a fungal toxin which inhibits sphingolipid biosynthesis in plants upon fungal
infection and also induces oxidative stress, suggesting that ANAC087 may be important in the regulation
of plant defense responses. Furthermore, both ANAC046 and ANAC087 were found to positively
regulate seed germination under abiotic stress conditions. This work illustrates the importance of these
three NAC transcription factors during natural and stress-induced senescence in Arabidopsis thaliana.
CURRICULUM VITAE:
Kashif received his B.Sc. (Hons) Agriculture degree in 2002 from the University of Agriculture,
Faisalabad, Pakistan. He obtained his M.Phil. Biotechnology from Quaid-i-Azam University, Islamabad,
Pakistan in 2005. He began his Ph.D. program in the laboratory of Dr. Stephen Rothstein in January,
2009.
PUBLICATIONS:
Shahzad K, Rauf M, Ahmed M, Malik ZA, Habib I, Ahmed Z, Mahmood K, Ali R, Masmoudi K,
Lemtiri-Chlieh F, Gehring C, Berkowitz GA and Saeed NA (2014). Functional characterisation of an
intron retaining K+ transporter of barley reveals intron-mediated alternate splicing. Plant Biology,
doi:10.1111/plb.12290.

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