MBGE SEMINAR by Onur Ízta■

Time: 09:30
Location: SCI 103

Speaker          :
Onur Özta■, Department of Biochemistry and Biophysics, Univ. of North Carolina Chapel Hill

Title                : Mechanisms in Plants to Overcome Environmental Stresses

Date                : June 17, 2019, Monday
Time               : 09:30   
Cookie & Tea: 09:15 SCI 103 
Place               : SCI 103  

Abstract         :

Plants have evolved numerous strategies to cope with environmental stresses influencing their growth and development. Among them is symbiotic nitrogen fixation developed by legumes to overcome nitrogen limitation in soil. Legumes enter a symbiotic interaction with rhizobia, soil bacteria that converts atmospheric nitrogen into usable ammonia. In root nodules, bacteria are internalized by host plant cells inside an intracellular compartment called the symbiosome and morphologically differentiate into nitrogen-fixing forms. We showed that the SYNTAXIN 132 (SYP132) gene in the model legume Medicago truncatula undergoes alternative cleavage and polyadenylation during transcription, giving rise to two t-SNARE protein isoforms. One of the isoforms, SYP132A, is a component of a nodule-specific secretory pathway required for the delivery of host proteins to the symbiosome. DNF2 is one of the host proteins being targeted to the symbiosome. We discovered that DNF2 belongs to a novel class of phosphatidylinositol-specific phospholipase C (PI-PLC) that cleaves proteins containing glycophosphatidylinositol (GPI), a glycolipid that is attached to the C-terminus of a protein to anchor the protein on cell membranes. DNF2 cleaves two GPI-anchored receptors, the release of which from the symbiosome membrane is essential to avoid defense responses that would otherwise eliminate bacteria from the host cell. During the establishment of symbiosis between legumes and rhizobia, the activity of DNF2 marks bacteria inside symbiosome as an ally, not an enemy.

Plants also encounter DNA-damaging environmental stresses such as ultra-violet (UV) component of solar radiation. They employ nucleotide excision repair to eliminate DNA lesions, so as to maintain their genome integrity and their fitness. This repair system detects a bulky DNA damage and removes the damage-containing oligomers by properly concerted dual (5’ and 3’) incision, followed by gap filling and ligation. We generated genome-wide single-nucleotide resolution excision repair maps of UV-induced DNA damage in Arabidopsis at different circadian time points and showed the effect of chromatin state, transcription and circadian clock on genome-wide kinetics of excision repair. We found that chromatin state influences the dynamics of repair. And, the joint actions of the circadian clock and transcription by RNA polymerase II control the repair of UV lesions for a large fraction of the genome. Our findings reveal very strong repair preference for the transcribed strands of active genes in Arabidopsis, and 30% of the transcription-coupled repair is circadian time-dependent. This dynamic range in nucleotide excision repair levels throughout the day enables Arabidopsis to cope with the bulky DNA lesion-inducing environmental factors including UV.