Abstract
Plants react to biotic and abiotic stresses with a variety of responses including the production of reactive oxygen species (ROS), which may result in programmed cell death (PCD). The mechanisms underlying ROS production and PCD have not been well studied in microalgae. Here, we analyzed ROS accumulation, biomass accumulation, and hydrocarbon production in the colony-forming green microalga Botryococcus braunii in response to several stress inducers such as NaCl, NaHCO3, salicylic acid (SA), methyl jasmonate, and acetic acid. We also identified and cloned a single cDNA for the B. braunii ortholog of the Arabidopsis gene defender against cell death 1 (DAD1), a gene that is directly involved in PCD regulation. The function of B. braunii DAD1 was assessed by a complementation assay of the yeast knockout line of the DAD1 ortholog, oligosaccharyl transferase 2. Additionally, we found that DAD1 transcription was induced in response to SA at short times. These results suggest that B. braunii responds to stresses by mechanisms similar to those in land plants and other organisms.
Highlights
Photosynthetic organisms support life on Earth by emitting oxygen as a byproduct of the photosynthetic process, and as a result these organisms face constant photo-oxidative stress (Ledford & Niyogi, 2005)
reactive oxygen species (ROS) production has been reported in plants and algae after treatment with several common stress inducers such as NaCl (Rao et al, 2007; Yilancioglu et al, 2014; Pancha et al, 2015), NaHCO3 (Gao et al, 2014), salicylic acid (SA) (Dorey et al, 1997; Gil et al, 2005), methyl jasmonate (MeJA) (Küpper et al, 2009), and acetic acid (Zuo et al, 2012a)
Using fluorescent staining to identify ROS production after a stress response (Fig. 1), our results show that B. braunii ROS production was triggered at short times (10 min) after treatment with all stress inducers
Summary
Photosynthetic organisms support life on Earth by emitting oxygen as a byproduct of the photosynthetic process, and as a result these organisms face constant photo-oxidative stress (Ledford & Niyogi, 2005). Most of the reactions involved in the capture of light energy are related to the production and control of reactive oxygen species (ROS) (Mittler et al, 2004; Hebelstrup & Møller, 2015). The equilibrium between light harvesting and energy production must be carefully controlled, otherwise the produced ROS may result in loss of protein function, deterioration of membrane integrity, and cell death (Ledford & Niyogi, 2005). Non-damaging levels of ROS may prepare cells to deal with higher ROS levels in order to survive this oxidative stress condition (Ledford & Niyogi, 2005).
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