identification of signaling factors involved in the regulation of alkaloid metabolism in n. tabacum

144 Pages·2017·0.75 MB·English

by  Nita Sachan

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2004
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Nita Sachan
University of Kentucky, [email protected]
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Sachan, Nita, "IDENTIFICATION OF SIGNALING FACTORS INVOLVED IN THE REGULATION OF ALKALOID
METABOLISM IN N. TABACUM" (2004). University of Kentucky Doctoral Dissertations. 442.
https://uknowledge.uky.edu/gradschool_diss/442
This Dissertation is brought to you for free and open access by the Graduate School at UKnowledge. It has been
accepted for inclusion in University of Kentucky Doctoral Dissertations by an authorized administrator of
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ABSTRACT OF DISSERTATION

Nita Sachan

The Graduate School

University of Kentucky

2004
IDENTIFICATION OF SIGNALING FACTORS INVOLVED IN THE
REGULATION OF ALKALOID METABOLISM IN N. TABACUM

____________________________________

ABSTRACT OF DISSERTATION
____________________________________

A dissertation submitted in partial fulfillment of the
requirements for the degree of Doctor of Philosophy in the
College of Agriculture
at the University of Kentucky

By
Nita Sachan

Lexington, Kentucky

Co-Directors: Dr. Deane Falcone, Assistant Professor of Agronomy
and Dr. George Wagner, Professor of Agronomy
Lexington, Kentucky
2004
Copyright (cid:211) Nita Sachan 2004
ABSTRACT OF DISSERTATION

IDENTIFICATION OF SIGNALING FACTORS INVOLVED IN THE
REGULATION OF ALKALOID METABOLISM IN N. TABACUM

To identify the signaling mechanisms and components that are involved in
regulation of a promoter for a gene involved in a secondary pathway I studied the
nicotinic alkaloid biosynthetic pathway using various N. tabacum tissues. Nicotine and
tropane alkaloids are widely known to be synthesized predominantly in the roots of
species that produce pyrrolinium ring containing alkaloids. Putrescine N-
methyltransferase (PMT) catalyzes the first committed step in the biosynthesis of these
alkaloid secondary products and earlier studies have indicated that PMT gene expression
is restricted to root tissue in Solanaceae plants. To further elucidate the factors that
govern the regulation of alkaloid synthesis, expression patterns dictated by the 5'-flanking
region of one of the members of the PMT -gene family, NsPMT3, using the b -
glucuronidase (GUS) reporter gene were examined. Various treatments were used to
characterize the nature of signaling in various tissues of seedlings, whole plants and
callus. High expression levels were detected in root tissue and no expression was detected
in leaves, in agreement with previous studies. However, mechanically wounded leaves
resulted in highly localized PMT expression. This wound-induced expression was
transient, with maximum levels occurring immediately after wounding and diminishing
after approximately 2–4 h. RT-PCR analysis of mRNA isolated from wild-type plants
also indicated upregulation of PMT expression in leaves upon wounding as well as very
low transcript levels in unwounded leaves. Low levels of PMT activity were detected in
leaf tissue, and this activity did not increase significantly upon wounding.
Transgenic callus material showed strong repression of PMT promoter activity in
the presence of light and auxin, whereas dark conditions and the absence of auxin
upregulated PMT promoter activity. Reactive oxygen species have been implicated in
signaling. When treated with the scavengers of reactive oxygen species (ROS),
dimethylthiourea (DMTU) or catalase, tobacco callus tissue, which displays highly
repressed alkaloid synthesis under normal culture conditions in the light, exhibited
significant induction of PMT promoter activity and alkaloid accumulation. It is thought
that light repression signals through an ROS intermediate to affect changes in alkaloid
pathway gene expression.
Upregulation of PMT-promoter activity was observed upon treatment with JA
(jasmonic acid) or darkness in roots of very young transgenic seedlings. Treatment with
auxin, salicylic acid (SA) and H O , on the other hand, was found to highly repress PMT
2 2
promoter activity. Action of other ROS such as nitric oxide and superoxide radicals on
PMT expression is not clear but probably play less of a role, compared to H O
2 2.

Consistent with this contention, treatment with light or glucose oxidase (GOX) and
glucose to generate H O also repressed alkaloid accumulation, and treatment of
2 2,
seedlings to dark conditions, the ROS scavenger DMTU, or jasmonic acid resulted in
alkaloid accumulation. Long distance signaling from leaves to roots is also suspected to
involve ROS, as leaves treated with GOX and glucose exhibited repressed PMT promoter
activity in roots. The responses of the PMT promoter to auxin, salicylic acid and HO
2 2
treatments were conserved as shown by similar responses of the N. tabacum PMT
promoter when examined in transgenic Arabidopsis, thereby suggesting that these
molecules signal through a conserved mechanism. Thus, ROS is strongly implicated in
acting as an intermediate in these signaling processes with HO proposed as a major
2 2
signaling component.

KEYWORDS: Alkaloids, putrescine N-methyltransferase, wounding, reactive oxygen
species, signaling in different tissues.

Nita Sachan
07/27/04
IDENTIFICATION OF SIGNALING FACTORS INVOLVED IN THE
REGULATION OF ALKALOID METABOLISM IN N. TABACUM

By

Nita Sachan

Deane L. Falcone
Co-Director of Disseration
George J. Wagner
Co-Director of Disseration
Arthur G. Hunt
Director of Graduate Studies
07/27/04
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Unpublished dissertations submitted for the Doctor’s degree and deposited in the
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Extensive copying or publication of the dissertation in whole or in part also requires the
consent of the Dean of the Graduate School of the University of Kentucky.
DISSERTATION

Nita Sachan

The Graduate School

University of Kentucky

2004
IDENTIFICATION OF SIGNALING FACTORS INVOLVED IN THE
REGULATION OF ALKALOID METABOLISM IN N. TABACUM

____________________________________

DISSERTATION
____________________________________

A dissertation submitted in partial fulfillment of the
requirements for the degree of Doctor of Philosophy in the
College of Agriculture
at the University of Kentucky

By
Nita Sachan

Lexington, Kentucky

Co-Directors: Dr. Deane Falcone, Assistant Professor of Agronomy
and Dr. George Wagner, Professor of Agronomy
Lexington, Kentucky
2004

Copyright (cid:211) Nita Sachan 2004
ACKNOWLEDGEMENTS

First of all I would like to thank my family, who have been the rock of my life. This work
would not have been possible without their love and sacrifice. My parents have been the guiding
force throughout my education and have always encouraged me to reach for higher goals. My
husband, Manish, for having made endless sacrifices to help me reach this stage. His research
ideas and intellectual stimulation has helped me tremendously. Biggest thanks to my five month
old daughter, Diya, who is now the shining light of my life, for her patience during writing of
this thesis.

My advisor and mentor, Dr. Deane Falcone, for his constant encouragement, guidance
and support throughout this thesis. This work would not have been possible without his
relentless efforts to guide me through new areas. I would also like to thank Dr. George Wagner,
for his constant encouragement and for constantly reminding me of the value of patience.
Thanks are also due to Dr. Arthur Hunt, Dr. Robert Houtz and Dr. Said Ghabrial for agreeing to
be on my Ph.D. committee and for their helpful suggestions. I am grateful to Dr. Harold Burton
for agreeing to be my external examiner.

Thanks are also due to all the past and present Falcone lab members. They have been
like my second family. This work would not have been possible without their support and
encouragement. In particular, I would like to thank Dr. Jingxian Zhang, for her help in coming
up with new ideas and Irinia Artiushin for her help in lab. I would also like to thank my other
lab members, Dr. Kil-Young Yun, Dr. Suchada Sukrong and Gabriela Diniello. It goes without
saying that I could not have survived my initial years at UK without the help of my dear friends
Annaps and Vigyan and my brother and friend, Sunil, have helped me get over the worst of
graduate school. There are so many others that I have not mentioned, to whom I am grateful for
their help and kindness throughout my stay at Lexington.

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