The United Nations has set “Zero Hunger” as its 2nd Goal of Sustainable Development. 815 million people today are suffering hunger and this number is expected to reach 2 billion by 2050. To meet these demands we need to increase food production. This can be achieved through arable land expansion or yield growth. As arable land becomes scarcer, we need to focus our efforts on increasing yield. The goal is to rethink agriculture.
Light limitation due to long-term shading by neighbouring plants is a major threat to food security, as it decreases overall yield. At high vegetation densities, shade-intolerant plants switch to a survival growth strategy known as the shade avoidance syndrome (SAS), which reconfigures overall architecture for optimal light capture. Of the diverse light-sensing photoreceptors that plants possess, phytochrome photoreceptors are exquisitely tuned to detect spectral changes indicative of nearby vegetation. These changes in light quality activate the phytochrome surveillance system, which in turn initiates compensatory changes in plant architecture and reproductive timing to suit more crowded conditions. Plants exhibiting SAS are characterised by elongation of growth of stem-like tissue, at the expense of harvestable organs (leaves, fruits, seeds, etc.). In nature, the SAS response is critical for plant survival, but it is troublesome for farmers, as it impacts crop robustness and yield. Interestingly, we have shown that the SAS response is tissue and developmental time-specific. For example, if shading occurs early in leaf development it leads to reduced cell numbers in leaf blades, and increased cell numbers in the leaf petioles. Whereas if this happens later in a leaf's life, it reduces the cell size in leaf blades and increases it in leaf petioles. Overall, the plant uses two alternative strategies to obtain the same result: small leaf blades and elongated petioles.
Several lines of research indicate that the shade signal is only perceived by plants at dusk, through a mechanism known as ‘gating’. Gating is controlled by the plant’s internal clock – namely the circadian clock. This endogenous timing mechanism allows a plant to fine-tune its physiology to a cyclical environment. Furthermore, proper internal timing that matches the environment is beneficial for plants and leads to optimised fitness and survival. However, almost nothing is known about how gating affects SAS plant fitness. Our data indicate that disruption of different elements that make up the clock results in plants that have an architecture very similar to SAS-affected plants. Furthermore, as the clock has been tied to the cell cycle, this suggests a possible mechanism through which the clock could be directly controlling the SAS leaf cellular response. Additionally, using a powerful bioinformatics approach we discovered an unexpected and potentially new avenue through which the clock and the phytochrome photoreceptors could be coordinately regulating leaf size, ultimately impacting biomass (a key predictor of crop yield).
TIME_FOR_SHADE is an innovative project, using genetic, bioinformatics, and dynamic imaging techniques to study how circadian clock gating affects plant fitness under light-limiting conditions and explore the mechanism that links the clock to the SAS leaf cellular response. Moreover, during the course of this action, we have established pennycress as a direct translational model. Identification of novel genetic targets to optimise plant yield under light-limiting conditions will be translated into pennycress, a newly domesticated oilseed crop. This will likely lead to increased crop yield and will inform other crop improvement efforts.
