Two sides to every leaf: how and why plants control stomatal distribution between leaf surfaces?

Objective

Plant leaves are polar organs with different upper (adaxial) and lower (abaxial) surfaces. Stomata are adjustable pores in leaves that allow CO2 influx for photosynthesis and mediate water loss via transpiration. These key structures that control plant survival and productivity are polarly localised only in leaf abaxial epidermis in most plants (hypostomaty). Some plants have stomata also on the upper leaf side; such amphistomatous plants should have a fitness advantage due to a better photosynthetic capacity. How is the making of adaxial stomata regulated and why are they present in a minority of plants, given their potential fitness advantage, remains a major unanswered question. I aim to design hypostomatous variants of the amphistomatous model plant Arabidopsis to address the role of adaxial stomata in plant physiology and fitness to answer two key questions: 1) how and why are adaxial stomata made, 2) how stomatal distribution between leaf surfaces is determined. I aim to do this via pursuing 3 specific goals: 1. Discover new regulators of adaxial stomatal development and evaluate the role of transcription factor SPEECHLESS in adaxial stomatal formation 2. Understand the role of adaxial stomata in plant physiology and fitness 3. Discover how stomatal distribution in leaves is set and regulated by environment and hormones I will use a balanced suit of untargeted and targeted approaches to identify the roles of new and known genes in the regulation of adaxial stomatal development and stomatal distribution between leaf surfaces, and understand the costs and benefits of adaxial stomata under different environmental conditions. I hope to answer the fundamental questions, how and why adaxial stomata are made, and hence explain why most species are hypostomatous. I expect the project will lead to a step-change in our understanding of plant stomatal biology and open up new horizons for designing leaf stomatal patterns to improve plant fitness under various environments