Simultaneous Suppression of Two Distinct Serotonin N-Acetyltransferase Isogenes by RNA Interference Leads to Severe Decreases in Melatonin and Accelerated Seed Deterioration in Rice

Abstract

Serotonin <i>N</i>-acetyltransferase (<i>SNAT</i>) is the penultimate enzyme in the melatonin biosynthetic pathway, in which serotonin is converted into <i>N</i>-acetylserotonin (<i>NAS</i>) in plants. To date, two <i>SNAT</i> isogenes with low amino acid sequence homologies have been identified. Their single suppression in rice has been reported, but their double suppression in rice has not yet been attempted. Here, we generated double-suppression transgenic rice (<i>snat1+2</i>) using the RNA interference technique. The <i>snat1+2</i> exhibited retarded seedling growths in conjunction with severe decreases in melatonin compared to wild-types and single-suppression rice plants (<i>snat1</i> or <i>snat2</i>). The laminar angle was decreased in the <i>snat1+2</i> rice compared to that of the wild-types and <i>snat1</i>, but was comparable to that of <i>snat2</i>. The reduced germination speed in the <i>snat1+2</i> was comparable to that of <i>snat2</i>. Seed-aging testing revealed that <i>snat1</i> was the most severely deteriorated, followed by <i>snat1+2</i> and <i>snat2</i>, suggesting that melatonin is positively involved in seed longevity.