The Strigolactone Pathway Is a Target for Modifying Crop Shoot Architecture and Yield

SIMPLE SUMMARY: Plants have developed the remarkable ability to sense their environment and modify their growth to suit changing conditions. This ability is integral for their survival and is facilitated by a range of plant hormones. Strigolactones (SLs) are one type of hormone that play an important role in plant growth response, where they are a key regulator of lateral branching. When growing conditions become poor, the production of SL increases, which reduces the number of branches a plant can make. Although this response may increase a plant’s chances of survival in the wild, it can have the unwanted effect of decreasing crop yield as the number of seed heads on a plant becomes reduced. It has been discovered that natural variations in the SL hormone pathway have been responsible for yield increases in staple crop varieties, such as rice and maize. We propose that new knowledge of the SL pathway and its effect on crop development can be applied using new technologies to develop crop lines with varied SL function, which may aid us in improving crop shoot architecture and yield across varying environments. ABSTRACT: Due to their sessile nature, plants have developed the ability to adapt their architecture in response to their environment. Branching is an integral component of plant architecture, where hormonal signals tightly regulate bud outgrowth. Strigolactones (SLs), being a novel class of phytohormone, are known to play a key role in branching decisions, where they act as a negative regulator of bud outgrowth. They can achieve this by modulating polar auxin transport to interrupt auxin canalisation, and independently of auxin by acting directly within buds by promoting the key branching inhibitor TEOSINTE BRANCHED1. Buds will grow out in optimal conditions; however, when conditions are sub-optimal, SL levels increase to restrict branching. This can be a problem in agricultural applications, as reductions in branching can have deleterious effects on crop yield. Variations in promoter elements of key SL-related genes, such as IDEAL PLANT ARCHITECTURE1, have been identified to promote a phenotype with enhanced yield performance. In this review we highlight how this knowledge can be applied using new technologies to develop new genetic variants for improving crop shoot architecture and yield.