Isolation and characterization of a 295-bp strong promoter of maize high-affinity phosphate transporter gene ZmPht1; 5 in transgenic Nicotiana benthamiana and Zea mays.

The small 295-bp ZmPht1; 5 promoter is sufficient to drive high-intensity expression of target genes, especially under phosphate deprivation conditions, and is therefore useful for crop improvement via transgenic techniques. Phosphate (Pi) deficiency has become a major challenge and limiting factor in world agricultural production. Manipulating the gene expression using appropriate promoters to improve the Pi absorption and utilization efficiency of crops could reduce the requirement for Pi fertilizers. In the study, a 295-bp strong promoter (M2P-7) of maize high-affinity phosphate transporter ZmPht1; 5 was isolated and functionally validated in transgenic Nicotiana benthamiana and maize by analyzing the ZmPht1; 5 promoter (M2P-1) and its 5' truncated variants (M2P-2 ~ M2P-8) in different sizes under normal and Pi-deprivation conditions. The M2P-7 displayed the highest promoter activities among 5' truncated fragments in all tested tissues of transgenic Nicotiana benthamiana at different development stages, which was 1.5 and 3 times higher than the well-used CaMV35S promoter under normal and Pi-deprivation conditions, respectively. In maize, the M2P-7 promoter activity was comparable to the maize ubiquitin1 promoter widely used in monocots under normal condition, which was about 1.3 times that of the ubiquitin1 promoter under Pi-deprivation environments. Moreover, the M2P-7 fragment is only 295 bp in length, thus reducing the construct size, and is therefore beneficial for genetic transformation. Thus, the small promoter M2P-7 of plant origin could be of great use for monocotyledonous and dicotyledonous crop improvement via transgenic techniques based on its promoter activities, expression patterns and small size.