We have frequently hypothesized that phytoplasmas
such as AY-WB produce effectors that manipulate
the phenotype of their hosts to their own benefit
(Hogenhout and Loria, 2008; Hogenhout et al., 2008;
Bai et al., 2009; Sugio et al., 2011). The recent discovery
and characterization of one such effector (SAP11)
offered support to this hypothesis, and the identification
of an additional effector (SAP54) that influences
the phenotype of host flowers lends further credence.
Nonetheless, the question of why phytoplasmas employ
effectors that (for example) alter the development
of flowers needs to be addressed. We have proposed
several possibilities (Sugio et al., 2011). One hypothesis
is that alterations in plant phenotype represent
an attempt by the phytoplasmas to encourage insect
activity (i.e. feeding and egg laying) as a means of
facilitating phytoplasma dispersal in the environment.
Phytoplasmas cannot survive outside of an insect or
plant host, and thus the movement of phytoplasmas in
natural (and agricultural) settings is dependent upon
their insect vectors. Phloem-feeding insects such as
leafhoppers may be attracted to plants that aggressively
produce young, green, vegetative tissues. Effectors
that increase the production of stems (such as
SAP11) or produce leafy flowers (such as SAP54) maystimulate leafhopper feeding, increasing the frequency
of phytoplasma acquisition by its vector. Another
possibility is that interfering with flower development
may extend the plant life span as annual plants die
upon seed production. In this scenario, phytoplasmas
that possess SAP54 or functionally similar effectors may
have a competitive advantage against those that do not
have these effectors. This study identifies a number of
excellent candidates that likely play important roles in
modulating host processes in both plants and insects,
and we expect many fascinating discoveries relating to
phytoplasma research in the near future.
We have frequently hypothesized that phytoplasmas
such as AY-WB produce effectors that manipulate
the phenotype of their hosts to their own benefit
(Hogenhout and Loria, 2008; Hogenhout et al., 2008;
Bai et al., 2009; Sugio et al., 2011). The recent discovery
and characterization of one such effector (SAP11)
offered support to this hypothesis, and the identification
of an additional effector (SAP54) that influences
the phenotype of host flowers lends further credence.
Nonetheless, the question of why phytoplasmas employ
effectors that (for example) alter the development
of flowers needs to be addressed. We have proposed
several possibilities (Sugio et al., 2011). One hypothesis
is that alterations in plant phenotype represent
an attempt by the phytoplasmas to encourage insect
activity (i.e. feeding and egg laying) as a means of
facilitating phytoplasma dispersal in the environment.
Phytoplasmas cannot survive outside of an insect or
plant host, and thus the movement of phytoplasmas in
natural (and agricultural) settings is dependent upon
their insect vectors. Phloem-feeding insects such as
leafhoppers may be attracted to plants that aggressively
produce young, green, vegetative tissues. Effectors
that increase the production of stems (such as
SAP11) or produce leafy flowers (such as SAP54) maystimulate leafhopper feeding, increasing the frequency
of phytoplasma acquisition by its vector. Another
possibility is that interfering with flower development
may extend the plant life span as annual plants die
upon seed production. In this scenario, phytoplasmas
that possess SAP54 or functionally similar effectors may
have a competitive advantage against those that do not
have these effectors. This study identifies a number of
excellent candidates that likely play important roles in
modulating host processes in both plants and insects,
and we expect many fascinating discoveries relating to
phytoplasma research in the near future.
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