Plant organ size and shape

Top: Arabidopsis (Left: wild-type. Right: PEAPOD deletion mutant)
Bottom: White clover (Left: PEAPOD deletion mutant. Right: wild-type) 

AgResearch has discovered and patented the PEAPOD gene, which allows certain traits to be altered to increase the usefulness or value of the plant.

The gene has a major influence on the size and shape of lateral determinant shoot organs, and regulates procambium and cambium activity. PEAPOD provides a method for increasing or decreasing the rate of vascular tissue production in plants by manipulating the gene. 

Loss or reduction of PPD function (expression) by deletion or gene silencing results in a higher level of cambial cell proliferation, and in turn increased vascular growth rates, more cambium, more phloem, more xylem (wood) and thicker stems. Conversely, over-expression of the PPD1 gene produces plants with reduced cambial activity, less xylem, less phloem and smaller stem diameter.
In woody plants the rate of cell production in the vascular cambium is the primary determinant of stem thickening and hence wood production. More rapid wood growth is a desirable trait in trees. Higher growth rates have the potential to reduce the growing period required to reach maturity/harvest dates, and also to increase yield per area of trees for the production of wood, paper, or plant biomass for biofuel.

In addition to positively regulating production of cambium, xylem and wood, it may be beneficial in some situations to reduce or slow production of cambium or xylem. Xylem is a lignin-rich tissue and lignin is relatively indigestable for grazing animals, so for forage applications there may be benefit in reducing the rate of production of xylem and lignin.

The ability to manipulate phloem production may also be beneficial. For example, more phloem may lead to a greater rate of carbohydrate accumulation in tuber plants such as potatoes.