Diurnal changes in the expression of genes that participate in phytosiderophore synthesis in rice

The roots of graminaceous plants secrete mugineic acid family phytosiderophores (MAs), allowing the acquisition of sparingly soluble iron (Fe) from the soil. In barley, the secretion of MAs occurs in a distinct diurnal rhythm. Rice also secretes deoxymugineic acid (DMA) in response to Fe deficiency, but it is unclear whether the secretion also occurs in a diurnal rhythm. A time course analysis with Northern blots was used to examine the expression of genes encoding enzymes in the MA biosynthetic pathway. The transcriptional levels of the NAS and NAAT genes fluctuated diurnally in Fe-deficient rice roots. These results suggest that, as in barley, the secretion of DMA in rice changes in a diurnal rhythm. Furthermore, the transcriptional levels of genes encoding translation initiation factor 4A2 (e1F4A2), ras-related small GTP-binding protein (GTPase), and ADP-ribosylation factor 1 (ARF1), which fluctuate diurnally in barley and are thought to be involved in the diurnal changes in HA secretion, also changed diurnally. As these genes are involved in intracellular vesicular transport, it is possible that secretion of DMA in rice is under the control of vesicular transport, as in barley root cells.