Truncated light-harvesting antenna 1
(
TLA1
) is a nuclear gene proposed to regulate the chlorophyll (Chl) antenna size in
Chlamydomonas reinhardtii
. The Chl antenna size of the photosystems and the chloroplast ultrastructure were manipulated upon
TLA1
gene over-expression and RNAi downregulation. The
TLA1
over-expressing lines possessed a larger chlorophyll antenna size for both photosystems and contained greater levels of Chl
b
per cell relative to the wild type. Conversely,
TLA1
RNAi transformants had a smaller Chl antenna size for both photosystems and lower levels of Chl
b
per cell. Western blot analyses of the
TLA1
over-expressing and RNAi transformants showed that modulation of
TLA1
gene expression was paralleled by modulation in the expression of light-harvesting protein, reaction centre D1 and D2, and VIPP1 genes. Transmission electron microscopy showed that modulation of
TLA1
gene expression impacts the organization of thylakoid membranes in the chloroplast. Over-expressing lines showed well-defined grana, whereas RNAi transformants possessed loosely held together and more stroma-exposed thylakoids. Cell fractionation suggested localization of the TLA1 protein in the inner chloroplast envelope and potentially in association with nascent thylakoid membranes, indicating a role in Chl antenna assembly and thylakoid membrane biogenesis. The results provide a mechanistic understanding of the Chl antenna size regulation by the
TLA1
gene.
Truncated Photosystem Chlorophyll Antenna Size in the Green Microalga Chlamydomonas reinhardtii upon Deletion of the TLA3-CpSRP43 Gene