Downregulation of GeBP-like α factor by MiR827 suggests their involvement in senescence and phosphate homeostasis

Leaf senescence is a genetically controlled degenerative process intimately linked to phosphate homeostasis during plant development and responses to environmental conditions. Senescence is accelerated by phosphate deficiency, with recycling and mobilization of phosphate from senescing leaves serving as a major phosphate source for sink tissues. Previously, miR827 was shown to play a significant role in regulating phosphate homeostasis, and induction of its expression was also observed during Arabidopsis leaf senescence. However, whether shared mechanisms underlie potentially common regulatory roles of miR827 in both processes is not understood. Here, we dissect the regulatory machinery downstream of miR827.

Overexpression or inhibited expression of miR827 led to an acceleration or delay in the progress of senescence, respectively. The transcriptional regulator GLABRA1 enhancer-binding protein (GeBP)-like (GPLα) gene was identified as a possible target of miR827. GPLα expression was elevated in miR827-suppressed lines and reduced in miR827-overexpressing lines. Furthermore, heterologous co-expression of pre-miR827 in tobacco leaves reduced GPLα transcript levels, but this effect was eliminated when pre-miR827 recognition sites in GPLα were mutated. GPLα expression is induced during senescence and its inhibition or overexpression resulted in senescence acceleration and inhibition, accordingly. Furthermore, GPLα expression was induced by phosphate deficiency, and overexpression of GPLα led to reduced expression of phosphate transporter 1 genes, lower leaf phosphate content, and related root morphology. The encoded GPLα protein was localized to the nucleus.

We suggest that MiR827 and the transcription factor GPLα may be functionally involved in senescence and phosphate homeostasis, revealing a potential new role for miR827 and the function of the previously unstudied GPLα. The close interactions between senescence and phosphate homeostasis are further emphasized by the functional involvement of the two regulatory components, miR827 and GPLα, in both processes and the interactions between them.