Lhcb Transcription Is Coordinated with Cell Size and Chlorophyll Accumulation (Studies on Fluorescence-Activated, Cell-Sorter-Purified Single Cells from Wild-Type and immutans Arabidopsis thaliana)

Abstract

To study the mechanisms that integrate pigment and chlorophyll a/b-binding apoprotein biosynthesis during light-harvesting complex II assembly, we have examined P-glucuronidase (CUS) enzyme activities, chlorophyll contents, and cell sizes i n fluorescenceactivated, cell-sorting-separated single cells from transgenic Arabidopsis thaliana wild-type and immufans variegation mutant plants that express an Lhcb (photosystem II chlorophyll a/b-binding polypeptide gene)/CUS promoter fusion. We found that CUS activities are positively correlated with chlorophyll content and cell size i n green cells from the control and immufans plants, indicating that Lhcb gene transcription i s coordinated with cell size in this species. Compared with the control plants, however, chlorophyll production is enhanced in the green cells of immufans; this may represent part of a strategy t o maximize photosynthesis in the green sectors t o compensate for a lack of photosynthesis in the white sectors of the mutant. Lhcb transcription is significantly higher in pure-white cells of the transgenic immufans plants than i n purewhite cells from norflurazon-treated, photooxidized A. fhaliana leaves. This suggests that immufans partially uncouples Lhcb transcription from its normal dependence on chlorophyll accumulation and chloroplast development. We conclude that immufans may play a role in regulating Lhcb transcription, and may be a key component in the signal transduction pathways that control chloroplast biogenesis.

Magnesium-dependent ATPase Activity and Cooperativity of Magnesium Chelatase from Synechocystis sp. PCC6803

“…Recent developments in intracellular signaling have increased interest in magnesium chelatase as a key component of a regulatory system (12,38). Magnesium chelatase activity is very sensitive to free magnesium concentration, and we have shown how the positive cooperativity depends on the extent of saturation with the other substrates.…”

The Mechanism of Variegation in immutans Provides Insight into Chloroplast Biogenesis

“…Nearly all molecular and biochemical studies on im have been conducted using fully expanded rosette leaves; for comparative studies, green versus white sectors have been obtained by dissection or via fluorescence-activated cell sorting (FACS) (Wetzel et al, 1994; Meehan et al, 1996; Aluru et al, 2009). Alternatively, all-green im leaves have been produced by altering light conditions during early seedling development (Rosso et al, 2009).…”

“…They also have elevated chl a/b ratios and enhanced chlorophyll amounts; FACS analyses have revealed these increases are due to elevated chloroplast numbers (per unit volume) rather than to enhanced amounts of chlorophyll per chloroplast (Meehan et al, 1996). Accompanying these changes, the anatomies of the green leaf sectors are reminiscent of leaves adapted to growth in high light conditions, e.g., they are thicker than normal due to enlarged air spaces, mesophyll cells, and epidermal cells (Aluru et al, 2001).…”

Chloroplast Photooxidation-Induced Transcriptome Reprogramming in ArabidopsisimmutansWhite Leaf Sectors

“…In contrast to these striking similarities, there are also differences. For example, transcription of Lhcb (as monitored by an Lhcb promoter:GUS transgene) is significantly more down-regulated in NF-treated versus imW cells, suggesting that retrograde signaling might be different in the two tissue types (Meehan et al, 1996).…”