Scientists at the RIKEN Center for Sustainable Resource Science in Japan
have found that the protein NGA1 is critical for plants to have normal
responses to dehydration. In plants, dehydration response is regulated by
the hormone abscisic acid (ABA). Successful rehydration requires
accumulation of ABA during the early stages of dehydration, among other
things. While scientists know how ABA does its work, they did not know much
about how ABA begins to accumulate in response to dehydration stress. RIKEN
scientist Hikaru Sato and his team screened 1,670 transgenic plants lines
and performed a series of experiments to address this issue.

The team found a plant line with an overexpression of NGA with a chimeric
repressor domain which resulted in reduced levels of the enzyme NCED3 during
dehydration stress. This was very promising because plants need NCED3 to
make ABA. The team hypothesized that NGA was a transcription factor that
could control the production of NCED3, and ultimately the biosynthesis of
ABA. They also found out that there is a whole family of NGA proteins, and
showed that all of them bind to the region of the NCED3 gene that triggers
its transcription.

The researchers then created transgenic plants for each member of the NGA
family and found that NGA proteins are naturally found in different parts of
plants, with different expression patterns during dehydration stress. The
timing of NGA expression also varied among different plant lines which meant
that not all of them function the same way during drought stress. From the
mutants they created, they found that after withholding water until the
plants withered, NGA1 mutants remained dried up and could not be revived
through rehydration. All the other mutants could be rehydrated.

[www.pnas.org]