| Abscission is the programmed organ separation from the main body of the mother plant. Separation takes place at predetermined positions called abscission zones. Although abscission is essential for the plant life cycle, the molecular regulation of abscission remains poorly understood. The rice grain shattering gene sh4, which encodes a putative MYB3 transcription factor, is involved in the development and function of the abscission zone between a rice grain and its pedicel. To investigate genes potentially regulated by sh4 during the abscission process, microarray analysis was conducted using sh4 transgenic plants. The study identified several categories of genes that were up-regulated by sh4. These include cell wall hydrolytic enzymes, expansins, pathogenesis-related genes, and abscisic acid (ABA) and stress responsive genes. Further studies indicated that exogenous ABA was capable of promoting flower abscission in wild rice species and the sh4 transgenic plants. ABA from the developing embryo may have served as the signal for the initiation of rice grain abscission. The study suggests that ABA is the hormone that signals rice grain abscission and sh4 is a regulator in the signaling pathway. |
