Activity, contribution, and regulation of seed pod photosynthesis

Abstract Although leaves are the primary sites of photosynthesis in most species, non-foliar organs are also photosynthetic. Non-foliar photosynthesis has been documented in a wide variety of species, however, understanding of this phenomenon has not progressed beyond its observation in many cases. Evidence supporting the requirement for non-foliar photosynthesis is absent or largely relies on manipulation of the environment or physical manipulation of the plant rather than genetic manipulation. In keeping with this, our understanding of the genetic mechanisms that control non-foliar photosynthesis relative to leaf photosynthesis is extremely poor. Arguably, our knowledge of seed pod photosynthesis has advanced further than other types of non-foliar photosynthesis, however, many questions remain outstanding. Here, we review the evidence supporting the activity and roles of seed pod photosynthesis. In addition, we discuss our knowledge of the regulatory mechanisms that control seed pod photosynthesis including the carbon and nitrogen transporters that shuttle resources to the seeds, mechanisms controlling differential dispersal of stomata between organs through leucine rich repeat protein activity, the timing of stomatal emergence controlled by a flower-specific transcription factor, and the differential organ activity of paralogous transcription factors that control leaf and seed pod chloroplast biogenesis. We also discuss how manipulation of seed pod photosynthesis may be used in isolation or in combination with modulations of vegetative photosynthesis to improve crop performance in terms of yield, nutrient requirements, and drought resilience.