Root-knot nematodes (Meloidogyne incognita) induce specific feeding sites in cucumber roots where they absorb
carbon nutrients from the host, thereby turning the feeding sites into a strong sink for assimilates.
Nematode infection may alter host
sugar metabolism in the roots of
sucrose-transporting species. However, much less is known about the species translocating
raffinose family
oligosaccharides (RFOs), such as cucumber. To address this knowledge gap, the dynamics of RFOs and
sucrose metabolisms, two major
sugar-metabolism processes, in cucumber roots during
nematode infection at transcription and
protein levels were analyzed. In the nematode-infected root, the expressions of RFO-synthesis genes, CsRS (
Raffinose Synthase) and CsGolS1 (
Galactinol Synthase 1), were upregulated at early stage, but were significantly decreased, along with CsSTS (
Stachyose Synthase), at the late stage during
nematode infection. By contrast, α-
galactosidase hydrolyzed RFOs into
sucrose and
galactose, whose encoding genes was suppressed (CsaGA2) at early stage and then elevated (CsaGA2, 4, and CsAGA1) at the late stage of
nematode infection. Consistently,
stachyose level was significantly increased by ∼2.5 times at the early stage but reduced at the late stage of
infection in comparison with the uninfected roots, with a similar trend found for
raffinose and
galactinol. Moreover, the genes encoding
sucrose synthase and cell wall
invertase, which are responsible for
sucrose degrading, were differentially expressed. In addition,
sugar transporter, CsSUT4, was enhanced significantly after
nematode infection at early stage but was suppressed at the late stage. Based on the observation and in connection with the information from literature, the RFOs play a role in the protection of roots during the initial stage of
infection but could be used by nematode as C nutrients at the late stage.