Constitutive expression of Arabidopsis LEAFY or APETALA1 genes in citrus reduces their generation time

Citrus trees have a long juvenile phase that delays their reproductive deve lopment by between 6 and 20 years, depending on the species. With the aim o f accelerating their flowering time, we transformed juvenile citrus seedlin gs to constitutively express the Arabidopsis LEAFY(LFY) or APETALA1 (AP1) g enes, which promote flower initiation in Arabidopsis. Both types of transge nic citrus produced fertile flowers and fruits as early as the first year, notably through a mechanism involving an appreciable shortening of their ju venile phase. Furthermore, expression of AP1 was as efficient as LFY in the initiation of flowers, and did not produce any severe developmental abnorm ality. Both types of transgenic trees flowered in consecutive years, and th eir flowering response was under environmental control. In addition, zygoti c and nucellar derived transgenic seedlings had a very short juvenile phase and flowered in their first spring, demonstrating the stability and inheri tance of this trait. These results open new possibilities for domestication , genetic improvement, and experimental research in citrus and other woody species.