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Functional genomics of

root growth and root signaling under drought

Funded by:

Under conditions of water deficit, roots transmit signals to leaves, which in turn reduce water usage. To understand more about the identity and transport of the long distance signals that plant roots transmit to shoots, we have embarked on a collaborative genomics project with groups at the Universities of Illinois and Missouri. We will profile a range of metabolites and the proteins in xylem sap in search of novel signals; we will also study gene expression profiles in the roots that are sending the signals. For more details on the project see: http://rootgenomics.missouri.edu/ .

Xylomics

Our focus on this project at the Danforth Center is to study the mechanisms of root to shoot signaling under water deficit through the integration of physiology, genomics, proteomics, and genetics.  Root signaling is an imortant area of study for agriculture because chemical signals control transpiration and growth at early stage of drought.
 

There are several key reasons for the identification of root signals:

• The nature of chemical signals is controversial.  A number of studies have implicated ABA, pH, nitrate and cytokinins as being important.  Other studies have shown that ABA is not important.

• The analyses of xylem sap are often not comprehensive so the interrelationship between substances in the xylem sap is not known.

• The identification of bona fide chemical signal may allow for engineering control over transpiration and growth upon drought

Aims

The major aim of xylomics is to investigate the production, identity, and transport of root signals.

• Profile composition of xylem sap in well watered and drought stressed plants

• Profile gene expression

• Integrate:

  • Changes in sap composition

  • Changes in root expression profiles

Progress in 2003-2004

We have developed a repeatable system for imposition of water stress.  Maize plants are grown for 16 days.  At that time, water was withheld from half of the pots.

• Soil Moisture is monitered using a PR-1 probe

• Leaf conductance is monitored using a porometer

• Leaf growth is monitored daily

• Leaf water potential in this experiment was measured 6 and 13 days after water was withheld.

Sap was collected at a point in time when chemical signals dominate and before changes in leaf water potential.  Day 7 was chosen for sap collection.

To determine where to collect sap, we conducted a preliminary experiment (see figure).

We analyze sap for the following: