Photoregulation of cellular morphology during complementary chromatic adaptation requires sensor-kinase-class protein RcaE in Fremyella diplosiphon

Abstract

We used wild-type UTEX481; SF33, a shortened-filament mutant strain that shows normal complementary chromatic adaptation pigmentation responses; and FdBk14, an RcaE-deficient strain that lacks light-dependent pigmentation responses, to investigate the molecular basis of the photoregulation of cellular morphology in the cyanobacterium Fremyella diplosiphon. Detailed microscopic and biochemical analyses indicate that RcaE is required for the photoregulation of cell and filament morphologies of F. diplosiphon in response to red and green light.

FIG. 1.

Cell morphologies of the WT and SF33 F. diplosiphon strains in GE-WL and RE-WL. Representative slices from a Z-series of DIC images of WL-adapted filaments of UTEX481 (A and B) and SF33 (C and D) were captured at a 40× oil immersion lens objective. Bars, 10 μm.

FIG. 2.

Morphological differences between F. diplosiphon strains in broad-band GL and RL. Representative slices from a Z-series of DIC images of GL- and RL-adapted filaments of UTEX481 (A and B), SF33 (C and D), FdBk14 (E and F), FdBk14/pPL2.7GWRcaE (G and H), and FdBk14/pPL2.7 (I and J) were captured at a 40× oil immersion lens objective. Bars, 10 μm.

FIG. 3.

Phycobiliprotein ratios and immunoblot analysis of RcaE accumulation in WT and SF33 strains, the FdBk14 mutant, and FdBk14 transformants. Upper panel, PE/PC ratios for F. diplosiphon strains. The colors of the bars indicate the colors of the illumination under which the cells were grown, and the bars represent the averages (± standard deviations) of results from three independent experiments. Lower panel, immunoblot results for RcaE accumulation in WT cells and FdBk14 cells either untransformed or transformed with pPL2.7 or pPL2.7GWRcaE during growth in GL or RL. A molecular mass marker is indicated to the left.

FIG. 4.

Phycobiliprotein autofluorescence of F. diplosiphon strains in broad-band GL and RL. Maximum-projection images from a Z-series of images of GL- and RL-adapted filaments of UTEX481 (A and B), SF33 (C and D), FdBk14 (E and F), and FdBk14/pPL2.7GWRcaE (G and H) were collected at a 63× oil immersion lens objective with a 2.5× zoom setting. Bars, 5 μm.

FIG. 5.

Median cell lengths and cell morphologies of F. diplosiphon strains in light-shifting experiments. Upper panel, bars represent the median cell lengths (in micrometers) calculated for a data set of at least 100 cells measured for UTEX481, SF33, and FdBk14 strains. Cultures were maintained in constant green (GG) or red (RR) light or shifted from GL to RL (GR) before being shifted back to GL (GRG) or shifted from RL to GL (RG) before being shifted back to RL (RGR). Lower panel, representative slices from a Z-series of DIC images collected at a 40× oil immersion lens objective with a 3× zoom setting. Numbers below the images are the ratios of A₅₆₀ to A₆₂₀ and are reported as an estimation of the ratios of PE to PC.