Effect of auxin on growth and accumulation of carbon reserves in the model green algae Chlamydomonas reinhardtii

MARÍA AGUSTINA DE MARCO; LEONARDO CURATTI; LARA SÁNCHEZ-RIZZA; MARTÍNEZ NOËL G; ARACELI BADER

Congreso; SAIB 2020; 2020

Microalgae are considered as a renewable energy source due to their high photosynthetic activity and rapid growth compared to higher plants and their ability to accumulate high content of carbon reserves (starch and neutral lipids). It is known that nutrients limitation and/or other triggers stimulate the accumulation of carbon reserves but at the expense of a growth slow down. Therefore, the study of the signal transduction pathways connecting growth and C-reserves synthesis is of great interest. The phytohormone auxin promotes plant cell growth, but its effect and the molecular mechanisms behind are poorly understood in green algae. In this study, we characterized the effect of indole-3 acetic acid (IAA) in the green algae Chlamydomonas reinhardtii (cc125). C. reinhardtii cells were cultivated at different concentrations of IAA (1, 3, 10 and 100 μg/ml) in complete TAP media, under nitrogen deficiency or without acetate in order to analyze the effect of IAA on different physiological conditions. Samples were taken at different time points to determine growth parameters (OD, number of cells, dry weight), cell volume and starch/total lipids/protein content. The results showed that AIA at 1μg/ml and 3 μg/ml concentration did not increase or slightly induced growth, respectively, regardless of the availability of nitrogen or acetate in the culture medium. Besides, no significant differences were found between control and auxin treatment on the accumulation of C-reserves. However, higher concentrations of IAA (10-100μg/ml) caused a decrease in growth and an increase in cell volume. High concentration of IAA also produced an increase in lipid and starch content as a per-cell-basis throughout the whole growth curve and after 24 h, respectively. Taken together, data suggest that high concentration of IAA at the beginning of the growth curve causes an arrest of cell division. On the other hand, if the auxin was added in an early stationary growth phase, the inhibitory growth effect did not occur. We also investigated the putative effect of IAA as inductor of protective mechanisms against different abiotic stresses, and preliminary experiments showed greater growth under oxidative stress in cultures pretreated with the auxin. In conclusion, the results of this study indicate that in C. reinhardtii, IAA acts as a negative growth regulator at high levels, possibly by decreasing cell division, but it does not have growth-promoting effect as in plants. It is important to highlight that the inhibition of growth triggered by high IAA appears to be general for green algae but not the growth-enhancing effect, response that may be species-specific. Future studies on IAA signal transduction, including synthesis and transport, the components of the transduction cascade itself and the expression of responsive genes, will be necessary for a more complete understanding of microalgal regulation of biomass production, as a feedstock for bioenergy and other applications.Supported by CONICET, ANPCyT (PICT2016-0173), UNMdP (EXA947/19) and FIBA.