Functional characterization of the PHT1 family transporters of foxtail millet with a novel Agrobacterium-mediated transformation procedure

Phosphate is an essential nutrient for plant growth and is acquired from the environment and
distributed within the plant in part through the action of phosphate transporters of the PHT1 family.
Foxtail millet (Setaria italica) is an orphan crop essential to the food security of many small farmers in
Asia and Africa and is a model system for other millets. A novel Agrobacterium-mediated transformation
and direct plant regeneration procedure was developed from shoot apex explants and used to
downregulate expression of 3 members of the PHT1 phosphate transporter family SiPHT1;2 SiPHT1;3
and SiPHT1;4. Transformants were recovered with close to 10% efciency. The downregulation
of individual transporters was confrmed by RT-PCR. Downregulation of individual transporters
signifcantly reduced the total and inorganic P contents in shoot and root tissues and increased the
number of lateral roots and root hairs showing they have non-redundant roles. Downregulation of
SiPHT1;2 had the strongest efect on total and inorganic P in shoot and root tissues. Complementation
experiments in S. cerevisiae provide evidence for the ability of SiPHT1;1, 1;2, 1;3, 1;7 and 1;8 to function
as high afnity Pi transporters. This work will aid development of improved millet varieties for global
food security.