Removal of redox-sensitive Rubisco Activase does not alter Rubisco regulation in soybean

Authors: Harvey, Christopher; CAVANAGH, AMANDA - University Of Illinois; KIM, SANG-YEOL - University Of Illinois; WRIGHT, DAVID - Iowa State University; EDQUILANG, RON - University Of Illinois; SHREEVES, KAYLA - University Of Illinois; PERDERMO, JUAN - University Of Central Lancashire; SPALDING, MARTIN - Iowa State University; ORT, DONALD - University Of Illinois; Bernacchi, Carl; HUBER, STEVEN - Retired ARS Employee

Submitted to: Photosynthesis Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2022
Publication Date: 9/27/2022
Citation: Harvey, C.M., Cavanagh, A.P., Kim, S., Wright, D.A., Edquilang, R.G., Shreeves, K.S., Perdermo, J.A., Spalding, M.H., Ort, D.R., Bernacchi, C.J., Huber, S.C. 2022. Removal of redox-sensitive Rubisco Activase does not alter Rubisco regulation in soybean. Photosynthesis Research. 154:169-182. https://doi.org/10.1007/s11120-022-00962-3.
DOI: https://doi.org/10.1007/s11120-022-00962-3

Interpretive Summary: Photosynthesis is the process that plants use to remove carbon dioxide from the atmosphere and incorporate it into plants to allow for growth. Enzymes are responsible for allowing this process to move forward. There are two enzymes that are involved in the first step, Rubisco which takes carbon dioxide out of the atmosphere and Rubisco Activase which turns Rubisco on and off. Previous research on laboratory grown species of plants show that changing Rubisco Activase can keep Rubisco turned on and allow for more photosynthesis and growth. This study worked with a food crop to see whether a similar response is seen in non-laboratory grown plants. The results show that changing Rubisco Activase does not improve plant growth, suggesting that other mechanisms for crop improvement are needed.

Technical Abstract: Rubisco activase (Rca) facilitates the catalytic repair of Rubisco, the CO2-fxing enzyme of photosynthesis, following periods of darkness, low to high light transitions or stress. Removal of the redox-regulated isoform of Rubisco activase, Rca-a, enhances photosynthetic induction in Arabidopsis and has been suggested as a strategy for the improvement of crops, which may experience frequent light transitions in the feld; however, this has never been tested in a crop species. Therefore, we used RNAi to reduce the Rca-a content of soybean (Glycine max cv. Williams 82) below detectable levels and then characterized the growth, photosynthesis, and Rubisco activity of the resulting transgenics, in both growth chamber and feld conditions. Under a 16 h sine wave photoperiod, the reduction of Rca-a contents had no impact on morphological characteristics, leaf expansion rate, or total biomass. Photosynthetic induction rates were unaltered in both chamber-grown and feld-grown plants. Plants with reduced Rca-a content maintained the ability to regulate Rubisco activity in low light just as in control plants. This result suggests that in soybean, Rca-a is not as centrally involved in the regulation of Rca oligomer activity as it is in Arabidopsis. The isoform stoichiometry supports this conclusion, as Rca-a comprises only~10% of the Rubisco activase content of soybean, compared to~50% in Arabidopsis. This is likely to hold true in other species that contain a low ratio of Rca-a to Rca-ß isoforms.