Ectopic expression ofJatropha curcas APETALA1(JcAP1) caused early flowering in Arabidopsis, but not in Jatropha

Abstract

Jatropha curcasis a promising feedstock for biofuel production because Jatropha oil is highly suitable for the production of biodiesel and bio-jet fuels. However, Jatropha exhibits a low seed yield as a result of unreliable and poor flowering.APETALA1(AP1) is a floral meristem and organ identity gene in higher plants. The flower meristem identity genes of Jatropha have not yet been identified or characterized. To better understand the genetic control of flowering in Jatropha, anAP1homolog (JcAP1) was isolated from Jatropha. An amino acid sequence analysis of JcAP1 revealed a high similarity to the AP1 proteins of other perennial plants.JcAP1was expressed in inflorescence buds, flower buds, sepals and petals. The highest expression level was observed during the early developmental stage of the flower buds. The overexpression ofJcAP1using the cauliflower mosaic virus (CaMV) 35S promoter resulted in extremely early flowering and abnormal flowers in transgenic Arabidopsis plants. Several flowering genes downstream ofAP1were up-regulated in theJcAP1-overexpressing transgenic plant lines. Furthermore,JcAP1overexpression rescued the phenotype caused by the Arabidopsis AP1 loss-of-function mutantap1-11. Therefore,JcAP1is an ortholog ofAtAP1,which plays a similar role in the regulation of flowering in Arabidopsis. However, the overexpression ofJcAP1in Jatropha using the same promoter resulted in little variation in the flowering time and floral organs, indicating thatJcAP1may be insufficient to regulate flowering by itself in Jatropha. This study helps to elucidate the function ofJcAP1and contributes to the understanding of the molecular mechanisms of flower development in Jatropha.