Kees van Loon talks with
ScienceWatch.com and answers a few questions about
this month's New Hot Paper in the field of Plant &
Article Title: Significance of inducible
defense-related proteins in infected plants
van Loon, LC;Rep,
Journal: ANNU REV PHYTOPATHOL
* Univ Utrecht, Fac Sci, Inst Environm Biol, NL-3508 TB
* Univ Utrecht, Fac Sci, Inst Environm Biol, NL-3508 TB
(addresses have been truncated)
Why do you think your paper is highly
This paper is a review on proteins that are induced in plants in response
to pathogen or insect attack and which may play a role in innate immunity.
The review was solicited by one of the editors of Annual Review of
Phytopathology on the grounds that the subject had not been reviewed
for quite some time. Many of such proteins belong to families, some members
of which are inducible through plant defense signaling routes, whereas
others are not.
Homologous proteins are widespread in nature but their functions are only
partially known. Data are published in widely different journals ranging
from basic molecular biology to applied disease control, and even in
medical journals related to developmental disorders and food allergy,
making it difficult for individual researchers to maintain a comprehensive
overview of the subject. Our paper draws much of this information together.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
The paper builds on previous reviews and summarizes the primary literature
from the last decade with emphasis on the different types of proteins and
their effects in plants. For the first time, we provided an overview of the
PR-1 family of pathogenesis-related (PR) proteins in
Arabidopsis and rice based on genome sequences,
together with the expression profiles of the Arabidopsis
proteins from micro-array data.
"The findings that various PR-proteins have
antimicrobial properties has prompted research to
develop transgenic plants with increased resistance
against a number of agronomically important
I found it important to illustrate that certain inducible defense-related
proteins when expressed in transgenic plants, can enhance resistance
against some pathogens but not against others, while they also act more
effectively in some plant species than in others. In the last few years, it
has become clear that effective pathogens have adapted to evade or suppress
plant defenses, and variation in defense signaling pathways and
antimicrobial proteins is a logical outcome of the specificity of
plant-pathogen interactions. The paper draws special attention to this
Would you summarize the significance of your paper
in layman’s terms?
Plants possess a range of sophisticated mechanisms to defend themselves
against different types of attackers, i.e., fungi, bacteria, viruses,
nematodes, and invertebrate and vertebrate herbivores. In response to an
attacker, a plant activates an appropriate set of defense mechanisms,
including a range of proteins with potential antimicrobial or
Seventeen families of specific PR-proteins have been established and there
are several additional defense-related proteins that can also play a role.
Many of these proteins are constitutively expressed in seeds, tubers, and
fruits as a defense against being eaten, and in humans can act as
allergens. Some of these proteins can also be induced by certain
non-biological stresses and help protect the plant against the effects of
e.g., wounding or freezing. Plants appear to possess large multi-gene
families of these proteins that are evolutionarily conserved and, hence,
must be important for plant functioning and survival.
How did you become involved in this research, and
were there any problems along the way?
I became involved when I did my Ph.D. research in the late 1960s and
discovered the PR-proteins by using the then-novel technique of
polyacrylamide gel electrophoresis. Since then, I continued, collaborating
with many researchers around the world, and initiated a series of
International Workshops on PR-proteins, starting in 1983 and continuing to
this day. Together with Thomas Boller, Vicente Conejero, and Stan
Pierpoint, I established a unifying nomenclature for PR-proteins in 1994.
Later, the interest shifted to the regulation of the induction of
defense-related proteins in general and their roles in plant innate
immunity and systemically induced resistance against subsequent invaders.
Following the initial description of the PR-proteins (LC van Loon and A van
Kammen, Virology 40, 199-211, 1970), I reviewed the subject in
1985 (LC van Loon, Plant Mol. Biol. 4: 111-116) and in 1999 (LC
van Loon and EA van Strien, Physiol. Mol. Plant Pathol. 55:
85-97), all papers that have been frequently cited. For the present review,
my colleagues Corné Pieterse and Martijn Rep generously offered to
cover the aspects of signaling and bioinformatics, respectively.
Where do you see your research leading in the
To maintain agricultural productivity while reducing reliance on chemical
crop protection, alternative ways to reduce plant diseases and pests are to
exploit natural mechanisms of plant defense. Stimulating plants through
application of certain microorganisms can prime plants to react more
effectively to a subsequent infection, a phenomenon called systemic
acquired resistance (SAR) or induced systemic resistance (ISR).
Although induced resistance does not fully protect, it is effective against
a wide spectrum of attacking organisms. Thereby, it provides an enhanced
level of basal resistance, in contrast to the effect of specific resistance
genes that act only against a particular attacker. Exploiting induced
resistance can reduce the need for other crop protection measures in a
durable and environmentally benign way.
Do you foresee any social or political
implications for your research?
The findings that various PR-proteins have antimicrobial properties has
prompted research to develop transgenic plants with increased resistance
against a number of agronomically important diseases. This strategy has
yielded crop species that are more resistant to various attackers. However,
because of consumer concerns, they have not been commercialized.
An alternative to circumvent genetic modification is the use of chemical or
biological inducers of systemic resistance. There are a few products on the
market that act in this fashion, but these are not widely used because they
only reduce, and do not prevent disease. Thus, their application is
restricted to niche markets where no other methods of crop protection are
effective. Yet, society could benefit greatly from judiciously combining
complementary strategies, including induced resistance, to obtain robust
and durable protection against plant pests and diseases.
Prof. dr. ir. L. C. “Kees” van Loon
Emeritus Professor of Phytopathology
Department of Biology
Utrecht, The Netherlands