Artificial microRNA (amiRNA) technology is now being tapped as the possible
new approach for the seed-specific gene silencing of the OsMRP5 rice gene in
hopes of engineering Low Phytic acid (LPA) rice. Phytic acid (PA) is the
major storage form of phosphorous (P) in cereal and legume seeds. However,
it is poorly digested by humans and monogastric animals and is regarded as
an anti-nutrient in food and feed. Transgenic rice with the mutated gene
OsMRP5 were developed and resulted in seeds with reduced PA content.
However, they also had reduced seed weight and viability.

The effectiveness of the amiRNA technology for the seed specific
down-regulation of OsMRP5 was evaluated based on changes of seed P content,
composition, and the agronomic performance of transgenic lines. Seed PA
contents were reduced by up to 71.9% in brown rice grains of transgenic
plants compared to control plants. There were also no significant
differences of plant height and number of tillers per plant observed between
the trangenics and the control.

However, the down regulation of OsMRP5 also resulted in increased inorganic
phosphorous (Pi) which is a known inhibitor to starch synthesis enzymes, in
the seeds. This resulted in significantly lower seed weights compared to
control plants, together with decreases in seed germination and seedling
emergence.

[link.springer.com]