The <i>PILNCR1</i>-miR399 Regulatory Module Is Important for Low Phosphate Tolerance in Maize

Abstract

The regulation of adaptive responses to phosphorus (P) deficiency by the <i>microRNA399</i> (<i>miR399</i>)/<i>PHOSPHATE2</i> (<i>PHO2</i>) pathway has been well studied in Arabidopsis (<i>Arabidopsis thaliana</i>) but not in maize (<i>Zea mays</i>). Here, we show that miR399 transcripts are strongly induced in maize by phosphate (Pi) deficiency. Transgenic maize plants that overexpressed <i>MIR399b</i> accumulated excessive amounts of P in their shoots and displayed typical Pi-toxicity phenotypes. We reannotated <i>ZmPHO2</i> with an additional 1,165 bp of the 5' untranslated region. miR399-guided posttranscriptional repression of <i>ZmPHO2</i> was mainly observed in the P-efficient lines. We identified Pi-deficiency-induced long-noncoding RNA1 (<i>PILNCR1</i>) from our strand-specific RNA libraries. Transient expression assays in <i>Nicotiana benthamiana</i> and maize leaf protoplasts demonstrated that <i>PILNCR1</i> inhibits ZmmiR399-guided cleavage of <i>ZmPHO2</i> The abundance of <i>PILNCR1</i> was significantly higher in P-inefficient lines than in P-efficient lines, which is consistent with the abundance of ZmmiR399 transcripts. These results indicate that the interaction between <i>PILNCR1</i> and miR399 is important for tolerance to low Pi in maize.