Fruit Crop Engineering with Igt Family Genes

Plant architecture influences many aspects of plant interaction with the environment. Thus, rational design of tree shape has major implications for genetic improvement of crop species. Branch orientation, or angle, is an understudied aspect of plant architecture that affects sunlight capture in shoots, and water uptake in the roots. Here we demonstrate the role of the IGT gene family in determining branch orientation in both shoots and roots in both Arabidopsis and dicotyledonous fruit crops. Two members of the IGT family, TILLER ANGLE CONTROL 1 (TAC1) and LAZY1, act antagonistically in the shoot to control lateral organ orientation. Loss of TAC1 results in strongly vertical shoot growth, seen in rice tillers, maize leaves, and Arabidopsis and Prunus lateral buds and branches. In contrast, loss of LAZY1 results in horizontal to prostrate growth. In the root, a third IGT gene, DEEPER ROOTING 1 (DRO1), controls root angles. Rice with a truncated DRO1 gene exhibit shallow angles across the root system. Our recent work shows that loss of DRO1 in Arabidopsis results in wide lateral root angles, consistent with the roles of TAC1 and LAZY1 in dicots versus monocot shoot organs. Overexpression of DRO1 in Prunus domestica (plum) results in longer root systems and the ability to root on shoot-growth culture media. IGT gene manipulation may provide important tools for bioengineering of desired plant shapes, above and below ground.