2.2 Wired connections between independent plants via
Dodder-mediated interspecific signaling
Dodder is a plant holoparasite that acquires water and nutrients from
host plants via the haustorium, which physically connects the parasite
to its host. Dodder species have broad host range, and can interconnect
several plant species or clusters of the same species (Figure 1) to
generate a common dodder network. The common dodder network can be
considered as an inter-plant highway that translocates large numbers of
proteins, RNA, metabolites, and plant viruses over a distance of at
least 100 cm (Hettenhausen et al. , 2017, Zhuang, Li, Song,
Hettenhausen, Schuman, Sun, Zhang, Li, Song & Wu, 2018). The common
dodder network can translocate more than 1,500 proteins between soybean
and Arabidopsis, and some of these proteins can localize in dodder
seeds. Approximately 15–30% of dodder proteins have host origin,
including transcription factors and R proteins that may function in
signal transaction. Dodder proteins can transfer to host plant cells.
Plants can anticipate future threats by receiving neighboring plant
signals transferred through the common dodder network. Although there
are few reports on the role of the common dodder network in inter-plant
signaling, the results indicate that these transferred signals are
important in biotic/abiotic stress responses. When a host of dodder
plant is under abiotic stress such high salinity, dodder transfers
salinity stress signals through a cluster of plants at a rate of 1.2 cm
per min, which prime salt tolerance in neighboring receiver plants. This
receiver plant priming changes the transcriptome, proline levels, and
stomatal conduction, so that the receiver plant stress response becomes
similar to that of the donor plant (Li, Zhang, Liu, Liu, Shen, Zhuang &
Wu, 2020b).
Plants infected with different herbivorous insects transfer relatively
long-distance signals to conspecific and heterospecific neighbors via
the common dodder network (Hettenhausen et al. , 2017, Zhuanget al. , 2018). Myzus persica infestation reduces the
contents of salicylic acid (SA) and jasmonic acid (JA) in dodder by up
to 58% and 41%, respectively. Aphids can modulate hormonal signaling
by injecting effector proteins into dodder plants (Rodriguez & Bos,
2013). Aphid-infested dodder induce JA but not SA in soybean hosts, and
subsequent phloem sap feeding by M. persica and chewing bySpodoptera litura causes 41% and 20% less damage, respectively,
in dodder-infected plants than in control plants. Dodder transfers
signals from insect-damaged soybean to conspecific or heterospecific
plants, such as tomato and Arabidopsis. Gene expression and RNA-seq
analyses reveal intense transcriptome modification in receiver plants.
An unknown signal can translocate between common dodder
network–connected Arabidopsis plants at a rate of 1 cm/min. A wave of
signal transduction propagated between connected Arabidopsis plants, as
intracellular WRKY 40 and WRKY53 transcription factors reached maximum
expression at 45 and 90 min after donor plant damage in the second and
fourth plants in the cluster, respectively (Zhuang et al. , 2018).