Gene for Promoting Parthenocarpy, Fertilization, and Fruit Size

Background: In seeded plants, successful fruit set and development are dependent on pollination, which can be highly sensitive to environmental conditions. Generating fruit without a requirement for physical pollination (parthenocarpy) allows extensive improvements in fruit crop productivity and yield.  Presently, it is known that adding gibberellic acid (GA) or auxin promotes parthenocarpy as well as eventual fruit size.  However, this mode of intervention requires physical treatment of fruit crops with these chemicals and the mechanisms through which these hormones promote fruit development remains unknown.  Creation of fruit bearing plants capable of undergoing parthenocarpy without a requirement for exogenous treatment with plant hormones would allow fruit growers to produce seedless varieties without the limitations of pollination or spraying crops with plant hormones.  Alternatively, some varieties of citrus fruits are naturally seedless and can develop without pollination.  Pollination in this case can be an impediment to production of the desired fruit and in this case generating plants less susceptible to pollination would be advantageous.

Technology Description: UCSD investigators have identified a novel three-gene clade, HAF, BEE1 and BEE3 genes, that controls the process of fertilization within the pistil/fruit.  This gene clade controls several critical functions within the developing pistil, including growth of the carpel.  HAF is necessary and sufficient to promote fertilization efficiency.  Overexpression of this gene is sufficient to promote parthenocarpy and increase fruit size without using exogenous plant hormones.  By placing the HAF gene under the control of a variety of unique promoters in plants, UCSD investigators have created transgenic lines that display parthenocarpy.  These transgenic lines have increased fertilization efficiency and also promote fruit growth. Reducing or eliminating the function of HAF causes less efficient movement of pollen tubes and reduced fertility.

Advantages:

• This technology represents the first gene identified that is capable of improving the likelihood of fertilization in pistils through increasing the efficiency of pollen tube movement.
• Fruit set depends on the successful completion of pollination and fertilization. Transgenic expression of HAF could enable fruit growers to induce parthenocarpy and increase fruit size without exogenous hormones or chemicals.
• Increased fruit size would increase the overall yield of the crop
• Seedless fruit

Applications:

• Some fruiting plants, such as tomatoes, are extremely sensitive to environmental conditions, in particular, to too low or high temperatures.  Tomato seed companies breed at different places in the world to develop cultivars suited for optimal fruit production under local climate conditions.  If fruit development could either be less dependent on efficient fertilization, or have efficiency increased under sub-optimal conditions, this could allow for increased fruit production in areas that are now unsuitable for efficient fruit set.
• In addition to tomatoes, genetic induction of parthenocarpy through the expression of this gene could greatly improve production of other difficult to fertilize or pollinate plants, including summer squash and other important food crops.
• Seedlessness is highly desirable trait in edible fruit with hard seeds such as pineapple, orange and grapefruit.  This technology would allow for the production and maintenance of seedless varieties of many such fruit crops.

Related Material: HALF FILLED promotes reproductive tract development and fertilization efficiency in Arabidopsis thaliana. Crawford BC, Yanofsky MF. Development. 2011 Jul;138(14):2999-3009.

Case Number: SD2010-018

Inquiries To: invent@ucsd.edu