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ARS Home » Plains Area » Fargo, North Dakota » Edward T. Schafer Agricultural Research Center » Cereal Crops Research » Research » Publications at this Location » Publication #392343

Research Project: Improvement of Biotic Stress Resistance in Durum and Hard Red Spring Wheat Using Genetics and Genomics

Location: Cereal Crops Research

Title: Plastid terminal oxidase is required for chloroplast biogenesis in barley

item Overlander-Chen, Megan
item Fiedler, Jason
item Carlson, Craig
item Yang, Shengming

Submitted to: Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2023
Publication Date: 11/21/2023
Citation: Overlander-Chen, M., Fiedler, J.D., Carlson, C.H., Yang, S. 2023. Plastid terminal oxidase is required for chloroplast biogenesis in barley. Plant Journal.

Interpretive Summary: Chloroplast development is tightly linked to photosynthesis which supplies food and energy for human population. However, chloroplast development is a very complex process, and the underlying mechanism has not been fully understood. In the present study, we cloned the Grandpa 1 (Gpa1) gene which regulates chloroplast formation in barley. Using map-based cloning strategy, we validated and characterized that the Gpa 1 gene encodes a plastid terminal oxidase (PTOX) in chloroplast. Loss of the PTOX activity increases the risk of photobleaching, which results in disruption of chloroplast development. Therefore, our research improved the understanding of the molecular mechanism underlying chloroplast biogenesis, and it provided knowledge for barley geneticists to potentially manipulate Gpa1 to optimize photosynthesis for higher yields.

Technical Abstract: Chloroplast biogenesis is critical for crop biomass and economic yield. However, chloroplast development is a very complicated process coordinated by cross-communication between the nucleus and plastids, and the underlying mechanisms have not been fully revealed. To explore the regulatory machinery for chloroplast biogenesis, we conducted map-based cloning of the Grandpa 1 (Gpa1) gene regulating chloroplast development in barley. The spontaneous mutation gpa1.a caused a variegation phenotype of the leaf, dwarfed growth, reduced grain yield, and increased tiller number. Genetic mapping anchored the Gpa1 gene onto 2H within a gene cluster functionally related to photosynthesis or chloroplast differentiation. One gene (HORVU.MOREX.r2.2HG0177270) in the delimited region encodes a putative plastid terminal oxidase (PTOX) in thylakoid membranes, which is homologous to IMMUTANS (IM) of Arabidopsis. The IM gene is required for chloroplast biogenesis and maintenance of functional thylakoids in Arabidopsis. Using CRISPR technology, we knocked out the PTOX-encoding gene and phenocopied the gpa1.a mutant. Therefore, HORVU.MOREX.r2.2HG0177270 is indeed the Gpa1 gene. Gene expression analysis revealed that the carotenoid biosynthesis pathway is suppressed in the gpa1 mutant, and that increased mitochondrial alternative oxidase (AOX) may compensate for the deficiency of PTOX activity. The cloning of Gpa1 not only improves our understanding of the molecular mechanisms underlying chloroplast biosynthesis, but indicates that the PTOX activity is conserved between monocots and dicots for the establishment of the photosynthesis factory.