March, 2008
Source:
CropBiotech Update
Scientists from the
Suranaree University of Technology in Thailand and
Louisiana State University
have developed transgenic tomato lines with increased resistance
to the common cutworm. The transgenic lines were modified to
express a potato gene coding for the enzyme polyphenol oxidase
(PPO). Polyphenol oxidase, which has also been implicated for
plant resistance to the bacterium Pseudomonas syringae catalyzes
the conversion of phenolics to quinones, plant secondary
metabolites that are involved in pathogen defense.
Growth rates of cutworm in the PPO-expressing lines were up to
three times lower compared to their non-transgenic counterparts.
Higher levels of PPO also resulted to increased larval
mortality, with the cutworm third instar consuming less foliage.
The results suggest a critical role for PPO-mediated phenolic
oxidation in pest resistance.
Article published by the Plant Journal at
http://dx.doi.org/10.1016/j.plantsci.2008.01.006
Source:
Plant Science
Volume 174, Issue 4, April 2008, Pages 456-466
Overexpression of tomato
polyphenol oxidase increases resistance to common cutworm
Siraprapa Mahanil(a), Jutharat Attajarusit(a), Michael
J.Stout(b) and Piyada Thipyapong(a)
(a)School of Crop Production Technology, Suranaree University of
Technology, 111 University Avenue, Muang District, Nakhon
Ratchasima 30000, Thailand
(b)Department of Entomology, 402 Life Sciences Building,
Louisiana State University, Baton Rouge, LA 70803, USA
Received 23 May 2007; revised 7 January 2008; accepted 11
January 2008. Available online 21 January 2008.
ABSTRACT
Polyphenol oxidases (PPOs),
which catalyze the oxidation of phenolics to quinones, have
been reported to confer resistance to Pseudomonas syringae
and are thought to be involved in insect resistance. To
assess the impact of PPO expression on resistance to the
common cutworm (Spodoptera litura (F.)) (Lepidoptera:
Noctuidae), we used transgenic tomato (Lycopersicon
esculentum Mill.) plants constitutively expressing sense-
and antisense-oriented potato PPO genes. Transgenic plants
expressing a sense PPO construct (overexpressing PPO [OP]
plants) exhibited 2.0–5.7-fold higher PPO activity levels,
whereas antisense PPO transgenic plants (suppressed PPO [SP]
plants) exhibited 1.5–7.3-fold lower PPO activity levels
than nontransformed controls. The PPO-overexpressing
transgenic plants clearly showed an increase in resistance;
simple growth rates of common cutworms on OP plants were up
to 2.5 and 3.3 times lower than on controls and SP leaves,
respectively, and larvae consumed less foliage. In addition,
increased PPO activity led to higher larval mortality. The
efficiency of conversion of ingested food and efficiency of
conversion of digested food of third instars were found to
be significantly different among tomato genotypes with
differing PPO activity levels, suggesting that PPO activity
rendered foliage less nutritious. Moreover, when leaflets at
nodes 4 and 8 of SP, NT and OP plants were detached and fed
to common cutworm larvae, their PPO activity levels were
induced 1.6–2.2-fold. These results suggest a critical role
for PPO-mediated phenolic oxidation in resistance to this
insect. Manipulation of PPO activity could provide
resistance simultaneously to both disease and insect pests,
and therefore might be used as a component of effective
integrated pest management.
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