Effect of ornithine decarboxylase and norspermidine in modulating cell division in the green alga Chlamydomonas reinhardtii

Abstract

The extensive genetic resources of Chlamydomonas has led to its widespread use as a model system for understanding fundamental processes in plant cells, including rates of cell division potentially modulated through polyamines. Putrescine was the major polyamine in both free (88%) and membrane-bound fractions (93%) while norspermidine was the next most abundant in these fractions accounting for 11% and 6%, respectively. Low levels of diaminopropane, spermidine and spermine were also observed although no cadaverine or norspermine were detected. Ornithine decarboxylase (ODC, EC 4.1.1.17) activity was almost five times higher than arginine decarboxylase (ADC, EC 4.1.1.19) and is the major route of putrescine synthesis. The fluoride analogue of ornithine (α-DFMO) inhibited membrane associated ODC activity whilst simultaneously stimulating cell division in a dose dependent manner. Following exposure to α-DFMO the putrescine content in the cells declined while the norspermidine content increased over two fold. Addition of norspermidine to cultures stimulated cell division mimicking the effects observed using DFMO and also reversed the inhibitory effects of cyclohexylamine on growth. The results reveal that ODC is the major route to polyamine formation in the Chlamydomonas CC-406 cell-wall mutant, in contrast to the preferential ADC route reported for Chlorella vulgaris, suggesting that significant species differences exist in biosynthetic pathways which modulate endogenous polyamine levels in green algae.

Alternative Splicing During theChlamydomonasreinhardtiiCell Cycle

“…Polyamines are ubiquitously present polycations that play important roles in cell growth and division in both prokaryotes and eukaryotes ( Minois et al 2011 ). They are important for sequestration of the negative charges of DNA and RNA, actin filament formation during spindle formation and cytokinesis ( Tassoni et al 2018 ). Polyamine levels in cells are regulated by their biosynthetic enzymes ( Gemperlová et al 2006 ).…”

Impact of nitric oxide on proline and putrescine biosynthesisin Chlamydomonas via transcriptional regulation

“…However, we cannot exclude the possibility that putrescine is accumulated, at least in part, due to other components. For example, the contribution of arginine decarboxylase to the formation of putrescine has been reported (Tassoni et al 2018). Interestingly, in Medicago truncatula, exogenous NO controls putrescine and proline content via enzymatic and transcriptional modulation of proline and polyamine biosynthetic pathways (Filippou et al 2013).…”

Polyamines in Microalgae: Something Borrowed, Something New

“…Recently, Tassoni et al detected ADC enzymatic activity in Chlamydomonas reinhardtii , even though the ADC gene is not present in its genome [75]. In general, ODC from the mouse, humans, plants, and some parasites is known to have a very strong preference for ornithine as a substrate [76,77,78].…”

“…TmSDS can also transfer aminopropyl groups to other polyamines such as NSpd, Spd, Cad, and Dap [92]. Based on analysis of protein structure, the gate keeper sequence of the substrate binding pocket (D173–F185) in HsSDS is very important for substrate selectivity [75]. Compared to HsSDS, a Pro has been replaced with an Ala at the gate keeper sequence of TmSDS, a substitution that is considered to increase the flexibility of substrate binding [93].…”

“…Notably, AtPUT homologs are present in almost all microalgal genomes (Table 2). Many microalgae can absorb and utilize polyamines from the environment, although the putative polyamine transporters have not been extensively studied [50,51,75,112,113,114]. Liu et al recently reported that Thalassiosira pseudonana can also secrete a variety of polyamines extracellularly [52], suggesting additional polyamine transporter may also exist in diatoms.…”