This thesis is focused on the chromosome-number studies in alveolate alga C. velia. This Apicomplexa-related photosynthetic organism proved to be a unique instrument for the study of Apicomplexa and their unique organelle apicoplast. To better understand the similarities and differences within these two phyla, a further chromosome analysis was needed. The first part of this thesis sums up the present knowledge about ploidy, life cycle and genome organization within C. velia and the close-relative phyla of Apicomplexa and Dinoflagellata. The second part describes our attempt to examine the ploidy and total number of chromosomes in C. velia using fluorescence in situ hybridization. The ploidy of C. velia was successfully determined and we also made a significant progress in the determination of the total chromosome number. (max. 4000 znaků)

Since its description in 2008, Chromera velia has drawn profound interest as the closest free-­-living photosynthetic relative of apicomplexan parasites that are significant pathogens, causing enormous health and economic problems. There-­- fore, this newly described species holds a great potential to understand evolu-­- tionary basis of how photosynthetic algae evolved into the fully pathogenic Apicomplexa and how their common ancestors may have lived before they evolved into obligate parasites. Hence, the aim of this work is to understand how C. velia function and respond to different environmental conditions. This study aims to reveal how C. velia is able to respond to environmental perturbations that are applied individually and simultaneously since, studying stress factors in separation fails to elucidate complex responses to multi stress factors and un-­- derstanding the systemic regulation of involved genes. To extract biologically significant information and to identify genes involved in various physiological processes under variety of environmental conditions (i.e. a combination of vary-­- ing temperatures, iron availability, and salinity in the growth medium) we pre-­- pared strand specific RNA-­-seq libraries for 83 samples in diverse environmental conditions. Here, we report the set of significantly differentially expressed genes as a re-­- sponse to the each condition and their combinations. Several interesting up-­- regulated and down-­-regulated genes were found and their functions and in-­- volved pathways were studied. We showed that the profound regulation of HSP20 proteins is significant under stress conditions and hypothesized that the-­- se proteins might be involved in their movements.

Nonphotochemical quenching is an important protective mechanism of photosynthetic proteins against excessive irradiation. In this work, isolation of native light harvesting antennae from alga Chromera velia was optimized using methods of sucrose density centrifugation, isoelectric focusing, ion exchange chromatography and gel electrophoresis. Moreover, the ability of light harvesting antennae to trigger nonphotochemical quenching was studied in vivo and in vitro.

A life cycle of many known algae is influenced by the circadian clock. It seems probable that also Chromera velia, the closest known photosynthetic relative to Apicomplexa, uses circadian oscillator. We tested, if fluctuating of zoospore?s abundance is driven by the circadian clock. This rhythm is stable even in the constant light condition. Furthermore, three cryptochrome genes, involved in circadian rhythms, were sequenced and consequently phylogenetically investigated. Two of them were classified as CRY-DASH, the third is CRY-DASH-like. The rhythmicity of CRY-DASH expression in C. velia was also investigated. The level of expression was also tested under constant light and dark condition. It was suggested that expression of these genes is associated with the circadian oscillator. This is the first study of the circadian clock in C. velia.