Tobacco 'antisense' Lines with a Stepwise Reduction in Rubisco Allowed a Network Approach to the Regulation of Photosynthesis, Metabolism, Allocation and Growth.

Over 2 decades ago, antisense rbcS tobacco lines with a progressive decrease in Rubisco abundance allowed network analysis of the regulation of photosynthesis, metabolism, and whole plant allocation. In the 1970 and 1980s, the study of the regulation of metabolism and growth was largely descriptive. Conceptual frameworks had been formulated that would allow a more rigorous approach, for example, to generate a small decrease in enzyme abundance and measure the resulting change in pathway flux. The lack of suitable mutants, however, made this approach practically impossible. This changed drastically when Agrobacterium-mediated transformation made it possible to alter expression of enzymes and other proteins at will. (Quick et al. in Planta 183:542–554, 1991a) and subsequent papers used antisense lines with a progressive decrease in Rubisco abundance to show that the contribution of Rubisco to the control of photosynthesis varies greatly, depending on the conditions in which photosynthesis is occurring and the conditions in which the plants had been grown. Analogous experiments by us and others on other Calvin–Benson cycle enzymes showed that they could also exert control and that the distribution of control depended on the conditions. We also used the rbcS antisense lines to, first, show that small decrease in Rubisco abundance is often accommodated by the photosynthetic apparatus to minimize the inhibition of photosynthesis and, second, explore how a larger decrease in Rubisco abundance and the resulting inhibition of photosynthesis impacts on central carbon and nitrogen metabolism, specialized metabolism, and whole plant architecture. This approach anticipated future developments like network analysis and system biology, is still relevant to designing strategies to improve crop photosynthesis, and can provide insights into photosynthetic performance and trade-offs in the field in a fluctuating environment.