## 4 Discussion
WRKY transcription factor family is of high interest since it is involved in diverse biotic/abiotic stress response and developmental/physiological processes [70]. Moreover, our data showed that the increase in _LCYB_ was concomitant with a rise in a lipid-associated protein CGP. It has a crucial role in maintaining the stability of \(\beta\)C-plastoglobules as it is localized at the periphery of the chloroplast [31; 32; 33], preventing the coalescence of the \(\beta\)-carotene globule, thanks to its hydrophilic layer, which covers the hydrophobic pigment core [33]. The gene coding for _CGP_ is present in four different copies in _D. salina_ 'Teodoresco' [32]. High light and/or nitrogen deficiency induces the accumulation of _CGP_ in _D. bardawil_ in parallel with \(\beta\)-carotene [33]. In accordance with our results, an increase in _CGP_ mRNA expression was noticed during the first hours of nitrogen deprivation of _D. bardawil_[32]. This increase was associated with an accumulation of triacylglycerlglycerol (TAG) and \(\beta\)-carotene [72]. _D. bardawil_ mobilizes TAG from the cytoplasm into the chloroplasts to form more plastoglobules [32]. In the non-carotenogenesis condition, the absence of these lipids globules was noticed. Heat shock protein (HSP70B) is a 70 kDa protein. It is a member of ATP-dependent molecular chaperones families, highly conserved and encoded by a single gene in green algae [73]. The increase in HSP70 expression lasting for 72 h of stress time can be explained by a cell requirement for chaperone molecule. A similar result was obtained by [PERSON] et al., 2001 [74], where the level of HSP70 gene expression increased immediately under irradiance stress by shifting cells from 75 to 2500 \(\mu\)mol photon. m\({}^{-2}\)-s\({}^{-1}\) among _D. salina_. Authors revealed that cells lost D1 protein by photodamage; thus, it would be replaced by the accumulation of HSP70B, which could afford conformational protection to the dissembled PSII core complex. In fact, protein misfolding is a process under oxidative and environmental stress, leading to an increase in molecular chaperone and protease expression [75]. The RPE catalyzes the reversible epimerization reaction of D-ribulose-5-phosphate into D-xylulose-5-phosphate in the Calvin cycle. During these first three days of stress, the level of its mRNA was significantly less expressed in stressed condition than in unstressed one after 72 h of stress. Similarly, but at the proteomic level, the amount of this enzyme was also decreased among _Dunaliella_ under stress [34] and among _Nannochloropsis oceanica_ under nitrogen deprivation [76]. This means that the photosynthetic efficiency is affected by nitrogen amount [76], but, at the same time, the down-regulation of this enzyme allows the accumulation of xylulose-5P, which probably would serve as a substrate for G3P production in the pentose phosphate cycle [34]. In order to identify if these transcriptional changes go along with posttranslational ones, bioinformatics tools were used to analyze protein sequences of the two genes (_CGP_ and _LCYB_) having the most increased transcriptional levels. Prediction of PTMs showed numerous possible phosphorylation, palmitoylation, and myristoylation sites, as well as sumoylation sites. Thes results corroborated the fine regulation of the two enzymes after their fold and the major regulatory role they have in modulating the ratio of carotenoid biosynthesis. Unlike plants, data concerning posttranslational regulation modalities of CGP and LCYB were not well studied for microalgae. In addition, the presence of SUMO protein in _Dunaliella_ was not reported previously. Posttranslational modification by SUMO is a major regulating mechanism for eukaryotic protein functions. SUMO becomes commonly covalently attached to specific targets (lysine residue) through a succession of molecular \"handoffs\" relating multienzyme cascades consisting of an E1 activating enzyme, an E2 conjugating enzyme, and an E3 ligase.