Modulation of the light-harvesting chlorophyll antenna size in Chlamydomonas reinhardtii by TLA1 gene over-expression and RNA interference

Abstract

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.

The mechanisms whereby the green alga Chlorella ohadii, isolated from desert soil crust, exhibits unparalleled photodamage resistance

“…This statement is supported by the following. The Chl a : b ratio in C. ohadii is naturally high, twice that found in C. sorokiniana and three‐ to four‐fold higher than that in other green algae such as C. vulgaris (Kowallik & Schürmann, ) and C. reinhardtii, and similar to that observed in the TLA1 mutant thereof (Mitra et al ., ). Chl b is associated with the light‐harvesting complexes; its low abundance in C. ohadii suggests a relatively small functional light‐harvesting cross‐section, which, unlike C. sorokiniana , did not change after exposure to high illumination (Fig.…”

Advances and challenges in genetic engineering of microalgae

“…A study with the truncated light‐harvesting antenna 1 (TLA1) gene, which is proposed to regulate the chlorophyll (Chl) antenna size in C. reinhardtii , showed that overexpressing and RNAi silencing modulate the expression of light‐harvesting protein, which provides a mechanistic understanding of the Chl antenna size regulation by this gene (Mitra et al . ). Moreover, inducing RNAi‐mediated silencing of the chlorophyllide an oxygenase (CAO) gene, chlorophyll b levels were partially reduced.…”

Biocommodities from photosynthetic microorganisms

“…In the model green alga C. reinhardtii, notable advances have enabled starch hyperaccumulation [87,103], reduction of light-harvesting antennae for more efficient light harvesting [104][105][106][107], and increased TAG accumulation in starchless mutants [86,87,[108][109][110]]. In the model diatom Phaeodactylum tricornutum, medium chain fatty acid synthesis and incorporation into TAG has been accomplished [83].…”