Nitric Oxide–Triggered Remodeling of Chloroplast Bioenergetics and Thylakoid Proteins upon Nitrogen Starvation inChlamydomonas reinhardtii 

Abstract

Starving microalgae for nitrogen sources is commonly used as a biotechnological tool to boost storage of reduced carbon into starch granules or lipid droplets, but the accompanying changes in bioenergetics have been little studied so far. Here, we report that the selective depletion of Rubisco and cytochrome b 6 f complex that occurs when Chlamydomonas reinhardtii is starved for nitrogen in the presence of acetate and under normoxic conditions is accompanied by a marked increase in chlororespiratory enzymes, which converts the photosynthetic thylakoid membrane into an intracellular matrix for oxidative catabolism of reductants. Cytochrome b 6 f subunits and most proteins specifically involved in their biogenesis are selectively degraded, mainly by the FtsH and Clp chloroplast proteases. This regulated degradation pathway does not require light, active photosynthesis, or state transitions but is prevented when respiration is impaired or under phototrophic conditions. We provide genetic and pharmacological evidence that NO production from intracellular nitrite governs this degradation pathway: Addition of a NO scavenger and of two distinct NO producers decrease and increase, respectively, the rate of cytochrome b 6 f degradation; NO-sensitive fluorescence probes, visualized by confocal microscopy, demonstrate that nitrogen-starved cells produce NO only when the cytochrome b 6 f degradation pathway is activated.

Algal Dual-Specificity Tyrosine Phosphorylation-Regulated Kinase, Triacylglycerol Accumulation Regulator1, Regulates Accumulation of Triacylglycerol in Nitrogen or Sulfur Deficiency

“…In contrast, parental wild-type cells showed chlorosis in these conditions. The large subunit of Rubisco (rbcL) and cytochrome f are rapidly degraded in N-deficient conditions (Wei et al, 2014). In contrast, tar1-1 cells maintained higher levels of these proteins in the same conditions (Fig.…”

A Nucleus-Encoded Chloroplast Phosphoprotein Governs Expression of the Photosystem I Subunit PsaC in Chlamydomonas reinhardtii

“…It is interesting to compare this response to a similar response that occurs under nitrogen limitation in Chlamydomonas with the downregulation of the cytochrome b 6 f complex. This latter response involves the coordinate degradation of the b 6 f complex itself, of proteins that regulate the expression of its chloroplast genes, and of proteins involved in its biogenesis (Raynaud et al, 2007;Wei et al, 2014).…”

“…For example, in Chlamydomonas, nitrogen deprivation leads to rapid decrease in the amount of cytochrome b 6 f complexes. This coordinate response involves the proteolytic degradation of its subunits and also of Mca1 and Tca1, nucleusencoded proteins that determine the stability and translation of petA mRNA, which encodes the Cytf subunit (Raynaud et al, 2007;Boulouis et al, 2011;Wei et al, 2014). The concerted response to nitrogen deprivation also involves other nucleusencoded proteins that take part in the assembly of the complex and its hemes (Wei et al, 2014).…”

“…This coordinate response involves the proteolytic degradation of its subunits and also of Mca1 and Tca1, nucleusencoded proteins that determine the stability and translation of petA mRNA, which encodes the Cytf subunit (Raynaud et al, 2007;Boulouis et al, 2011;Wei et al, 2014). The concerted response to nitrogen deprivation also involves other nucleusencoded proteins that take part in the assembly of the complex and its hemes (Wei et al, 2014). An early response of Chlamydomonas to iron deprivation is the downregulation of PSI and the remodeling of its light-harvesting antenna (Moseley et al, 2002;Naumann et al, 2005).…”

Sulfur deprivation-induced expression of THB1, a Chlamydomonas reinhardtii truncated hemoglobin, is mediated by nitrate reductase-dependent NO production

“…NO has also been recognized as a player in various signaling pathways in Chlamydomonas, including cell death (Yordanova et al, 2010), remodeling of chloroplast bioenergetics upon nitrogen starvation (Wei et al, 2014), regulation of nitrate assimilation (Sanz-Luque et al, 2013), anaerobic acclimation (Hemschemeier et al, 2013) and salt stress (Chen et al, 2016). In this unicellular alga, NO is also found to act as a signaling molecule for the transcriptional regulation of several S-responsive genes upon sulfur deprivation (Minaeva et al, 2017;Zalutskaya et al, 2018).…”