Fig. 5: Change in the mRNA and rRNA levels of the nucleus of Chroomonas sp. after ingestion by N. aeruginosum.

a Schematic diagrams showing the coculture of N. aeruginosum and Chroomonas sp. Dc01 used to investigate the change in mRNA and rRNA levels of Chroomonas sp. ingested by N. aeruginosum in (b–d). Chroomonas sp. Dc01 was removed from the coculture for N. aeruginosum cells to digest most of the kleptoplasts derived from Chroomonas sp. (~95% and 60% of N. aeruginosum cells had completely digested the nucleus and kleptoplast derived from Chroomonas sp., respectively). The starved N. aeruginosum cells were again fed Chroomonas sp. until ~60% of the cells had ingested Chroomonas sp. Then, the free-living Chroomonas sp. was removed from the coculture (day 0) and N. aeruginosum cells with kleptoplasts were cultured for 12 days under continuous light (10 µmol photons m⁻² s⁻¹). b Change in N. aeruginosum cell number after the removal of free Chroomonas sp. c Histogram showing the change in the ratio of N. aeruginosum cells possessing cryptomonad nuclei and the number of the nuclei per cell. d RT-qPCR showing the changes in mRNA levels per Chroomonas sp. nucleus of LHC1 (LIGHT HARVESTING COMPLEX 1), PSBM, PETC, FBA, APX, RPL10, ACTIN, and TUBULIN A mRNAs, and 18S rRNA, upon and after ingestion. The values were normalized with that of an internal control, which was equivalent to the culture volume, and the number of Chroomonas sp. nuclei per culture volume. The averaged value of free-living Chroomonas sp. was defined as “1.0.” The levels in the free-living Chroomonas sp. were determined in the culture immediately after the addition of Chroomonas sp. to the starved N. aeruginosum culture. The error bars represent standard deviation (four independent cultures). *P < 0.05; N.S., no significant difference (t-test).