Photosynthesis is an indispensable process that provides the oxygen we breathe, regulates climate, and drives biological processes including crop yields. An important and obvious challenge for crop improvement is: Is photosynthesis and its regulation in crops amenable to improvement to stimulate yields? If so, how could this be done? Photosynthesis is a well-studied process with models of the limitations in the photosynthetic pathway (Zhu et al., 2010). The past 10 years have seen a major effort into improving photosynthesis with a justification that improvements in crop yields need to be quick and large because of the yield plateauing of major crops. The harvest index has been optimized, and therefore, the next bottleneck is proposed as photosynthesis. However, crop yields are yet to benefit from this research despite some tantalizing examples of genetic interventions in models (Arabidopsis and tobacco) including field studies (Glowacka et al., 2018; South et al., 2019). The focus on photosynthesis has been controversial given long-standing evidence with well-reasoned arguments going back to the 1970s that carbon input is not limiting for crop growth and yield (Sinclair et al., 2019). Failure to produce tangible benefits in crops so far from the photosynthetic research effort is attracting gathering criticism (Araus et al., 2021) with arguments for a more balanced approach (Reynolds et al., 2021). However, a recent study overexpresses Rubisco in paddy rice which increases yield in the field under good nitrogen supply by 17–28% (Yoon et al., 2020). This appears to be the first successful direct targeting of photosynthesis in the field in a major food security cereal crop. This article gathers information from recent literature on the photosynthetic improvement of both heavily reductionist approaches and broader-based strategies to provide a balanced opinion of the way forward for the photosynthesis field for crop yield improvement.
