Identification and expression profiling of phosphate stress responsive genes in maize

Abstract

The post green revolution agriculture is based on generous application of fertilizers and high-yielding genotypes. Maize cannot utilize more than 10% of the applied inorganic phosphate (Pi) which is a non-renewable fertilizer resource. Owing its emergence as an industrial, feed and food crop, improvement in phosphorus use efficiency (PUE) is highly essential in maize for sustainable use of phosphate containing fertilizers. Therefore, there is a need to identify key regulatory genes playing pivotal role in acquisition, transportation and utilization of Pi in maize. In this endeavor, the present study was undertaken to identify Pi-responsive genes in maize through whole-genome analysis and expression profiling. The twelve Pi-responsive genes (five having regulatory role, four encoding for secretory proteins and two encoding for Pi transporters) were identified through Hidden Markov Model-based homology search. The expression of identified genes in root and shoot tissues of hydroponically grown maize inbred line HKI-163 under Pi sufficient (1mM KH2PO4) and deficient (5µM KH2PO4) condition was analyzed using quantitative and semi-quantitiative RT-PCR. Expression analysis revealed that 11 out of 12 genes were significantly up or down regulated under Pi-deficient condition. To comment upon the mechanism of observed differential expression of Pi-responsive genes under phosphate deprived condition, cis-regulatory elements present in the upstream promoter region of these genes were analyzed and phosphate responsive elements were found in two genes. In other genes, the differential expression may be indirectly linked to phosphate deprivation. We believe that the identified Pi-responsive genes can be employed for engineering high PUE in maize after functional validation.