Identification and Analysis of Genes Involved in Tetrapyrrole Metabolism and Plastid-Derived ROS-Mediated Signaling in Chlamydomonas Reinhardtii

The tetrapyrrole biosynthesis (TBS) is tightly controlled at the transcriptional and the posttranslational level. Due to photooxidative stress caused by accumulating tetrapyrrole intermediates, multiple factors are required for a fine-tuned metabolic flow in the pathway. In the previous funding period , we generated a multitude of (i) pigment and (ii) ROS-signaling mutants with modified light sensitivity, photosynthetic capacity, disrupted chlorophyll biosynthesis in dark or in light as well as deregulated tetrapyrrole-induced chloroplast-to-nucleus signaling and began an initial biochemical and genetic analysis of several mutants. In our research we use the unicellular green algae Chlamydomonas reinhardtii, a model organism to study genetic, physiological, and biochemical processes. Many of the findings based on C. reinhardtii studies can be directly applied to facilitate research in plants and animals system. There are two important advantages of using C. reinhardtii specifically in our studies on TBS. Firstly, this organism is able to grow heterotrophically, both in dark and light, given that a reduced carbon source is provided. Thus, mutants of C. reinhardtii with a complete block in chlorophyll biosynthesis and photosynthesis can be successfully studied. Secondly, C. reinhardtii produces chlorophyll in darkness, which is an obvious advantage considering light sensitivity of the intermediates-accumulating TBS mutants.
The aim of the continuing project is to characterize the function of the identified new genes for proteins involved in (i) TBS and (ii) tetrapyrrole-generated 1O2-signaling. We, firstly, intend to explore the regulatory function in TBS of the already identified mutant genes and to examine additional mutants with promising phenotypes, when the mutant gene is identified and the mutant successfully complemented. Secondly, after monitoring the 1O2-dependent retrograde signaling in chlorophyll-free mutants and identification of these mutant genes, it is aimed to correlate the function of the mutant gene product with the plastid-derived 1O2-signaling.
The rationale behind the reverse and forward genetics studies are based on many unknowns in TBS and retrograde signaling in C. reinhardtii, such as (i) the diverse control of light-dependent and light-independent chlorophyll biosynthesis, the need of controlled, stable and low steady-state levels of photoreactive TBS intermediates, and the necessity of the avoidance of metabolite accumulation upon illumination by means of transcriptional and posttranslational regulation and (ii) the elimination and signaling process of 1O2 generated by accumulation of tetrapyrroles and originated photosystem II and I. Our hypothesis is that not the tetrapyrroles, but either scavenging enzymes or 1O2-binding protein could play a role in the plastid-derived signaling and could be identified by the proposed second site mutant screen.

Principal Investigators
Grimm, Bernhard Prof. Dr. rer. nat. Prof. Dr. (Details) (Plant Physiology)

Duration of Project
Start date: 07/2019
End date: 07/2021

Research Areas
Plant Physiology

Research Areas
Pflanzliche Molekularbiologie

Last updated on 2021-04-01 at 17:50