The shade-avoidance syndrome is a complex and poorly understood set of reactions whereby plants sense and compete with their neighbors for light.

—Udaya Kalluri, a member of ORNL’s Environmental Sciences Division

Through this project, ORNL researchers and partners hope to understand the impacts of the shade-avoidance on plant productivity as the tree directs resources toward stem elongation and away from harvestable portions of the tree. Such basic research has important implications for maximizing carbon capture per unit land area.

Recent increases in energy costs have led to a heightened interest in growing hybrid poplar (Populus spp.) for ethanol production. Available commercial clones, however, represent only one or two generations of genetic improvement over their wild ancestors. Alteration of plant architecture (i.e., canopy form) was a major component of the striking gains in agronomic productivity achieved during the green revolution. In particular, the development of plants that are unresponsive to limited light availability via an altered phytochrome response has been an effective strategy for maximizing productivity in high-density stands. Therefore, the objective of this project is to gain a molecular understanding of phytochrome-mediated responses to competition in Populus and then use that knowledge to maximize carbon capture per unit land area.

—Project abstract

ORNL researchers Jerry Tuskan, Stan Wullschleger and Kalluri plan to harness the recently sequenced Populus genome to learn more about the molecular action of phytochromes, photoreceptors through which plants perceive their light environment. Ultimately, this work will lead to a conceptual model of how plants compete for light and contribute to the development of high-yielding plant varieties that maintain productivity in dense stands.

Specifically, the project will we seek to explore:

1. The genes and gene networks associated with the shade-avoidance syndrome;

2. The relative roles of the various phytochrome photoreceptors in the shade-avoidance syndrome; and

3. The correlation between sequence variations in phytochrome genes and quantitative variation in a set of characteristic shade avoidance features (phenotype).

Resources:

• A Functional Genomics Approach to Altering Crown Architecture in Populus: Maximizing Carbon Capture in Trees Grown in Dense Plantings