Soybean proteins GmTic110 and GmPsbP are crucial for chloroplast development and function

Authors: Sandhu, Devinder; ATKINSON, TAYLOR - University Of Wisconsin; NOLL, ANDREA - University Of Wisconsin; JOHNSON, CALLIE - University Of Wisconsin; ESPINOSA, KATHERINE - Iowa State University; BOELTER, JESSICA - University Of Wisconsin; ABEL, STEPHANIE - University Of Wisconsin; DHATT, BALPREET - University Of Wisconsin; SINGSAAS, ERIC - University Of Wisconsin; SEPSENWOL, SOL - University Of Wisconsin; GOGGI, SUSANA - Iowa State University; PALMER, REID - Iowa State University

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2016
Publication Date: 11/14/2016
Publication URL: http://handle.nal.usda.gov/10113/5317267
Citation: Sandhu, D., Atkinson, T., Noll, A., Johnson, C., Espinosa, K., Boelter, J., Abel, S., Dhatt, B.K., Singsaas, E., Sepsenwol, S., Goggi, S., Palmer, R. 2016. Soybean proteins GmTic110 and GmPsbP are crucial for chloroplast development and function. Plant Science. 252:76-87 doi: 10.1016/j.plantsci.2016.07.006.

Interpretive Summary: Plants use sunlight to make sugars through the process of photosynthesis. Despite the importance of photosynthesis, the understanding of the functions of the genes involved in the process is still deficient. Chlorophylls are essential pigments that play a crucial role in the photosynthesis process by absorbing sunlight. Identification and characterization of genes involved in chlorophyll synthesis are important to improve agricultural productivity. We have identified two yellow (chlorophyll deficient) mutant plants in soybean; one is viable and the other one is lethal, that dies after two weeks of germination. We named these mutants as viable-yellow and lethal-yellow. Both the mutants were compromised for their chlorophyll content and in their ability to use sunlight for photosynthesis. The mutants showed impaired structure and function of chloroplast, the main organelle involved in photosynthesis. The genes responsible for these mutations were identified by generating genetic maps. The viable-yellow trait was due to a mutation in a transporter protein (Tic110) in the chloroplast membrane. The lethal-yellow trait was due to a mutation in a protein (PsbP) involved in assembly of pigments required for absorption of sunlight. Functional characterization of these proteins is an important step forward in understanding the complex photosynthesis process and enhancing basic understanding about the process. Findings of this investigation will be valuable to plant physiologists, geneticists and plant breeders in developing approaches to control photosynthesis for enhanced production of food, fiber and energy.

Technical Abstract: We have identified a viable-yellow and a lethal-yellow chlorophyll-deficient mutant in soybean. Segregation patterns suggested single-gene recessive inheritance for each mutant. The viable- and lethal-yellow plants showed significant reduction of chlorophyll a and b. Photochemical energy conversion efficiency and photochemical reflectance index were reduced in the viable-yellow plants relative to wildtype, whereas the lethal-yellow plants showed no electron transport activity. The viable-yellow plants displayed reduced thylakoid stacking, while in the lethal-yellow plants, proplastids failed to differentiate into chloroplasts with thylakoids and grana. Genetic analysis revealed recessive epistatic interaction between the viable- and the lethal-yellow genes. The viable-yellow gene was mapped to a 58 kb region on chromosome 2 that contained 7 predicted genes. A frame shift mutation due to a single base deletion in Glyma.02g233700 resulted in an early stop codon. Glyma.02g233700 encodes a translocon in the inner membrane of chloroplast (GmTic110) that plays a critical role in plastid biogenesis. The lethal-yellow gene was mapped to an 83 kb region on chromosome 3 that contained 13 predicted genes. Based on the annotated functions, we sequenced three potential candidate genes. A single base insertion in the second exon of Glyma.03G230300 resulted in a truncated protein. Glyma.03G230300 encodes for GmPsbP, an extrinsic protein of Photosystem II that is critical for oxygen evolution during photosynthesis. GmTic110 and GmPsbP both displayed highly reduced expression in the viable- and lethal-yellow mutants, respectively. The yellow phenotypes in the viable- and lethal-yellow mutants were due to the loss of function of GmTic110 or GmPsbP resulting into photooxidative stress.