Pearl millet, Pennisetum glaucumL.), a crop of semi-arid tropics,
has remarkable tolerance to a wide range of abiotic stresses,
including high degree of genetic diversity for drought stress
tolerance. To investigate the molecular mechanisms that possibly
account for differences in drought tolerance, four recombinant
inbred lines from a high resolution cross (HRC) were
selected for their variability in transpiration rate (Tr) response
to vapour pressure deficit (VPD) conditions. The expression
of PgAQPs in contrasting genotypes varied during the day,
generally decreasing in the afternoon regardless of the VPD
conditions. However, under high VPD conditions (4.21kPa),
both root and leaf tissues of the VPD-insensitive genotypes
had higher transcript abundance than the VPD-sensitive genotypes.
Three PIP2 subfamily genes (PIP2;1, PIP2;3 and PIP2;6)
particularly PIP2;6 gene, showed an increase in transcript
abundance under high VPD conditions. Transgenic tobacco
plants constitutively expressing PgPIP2;6 gene were developed
for functional validation studies in homozygous T2 transgenic
tobacco plants. The transgenic plants showed better tolerance
under drought stress, VPD and salinity compared to wild type
plants as seen from biochemical, physiological and molecular
studies. The transgenic plants also showed increased soluble
sugar, membrane stability, reduced electrolyte leakage and
other photosynthetic parameters as compared to the wild type
(WT). Taken together, our studies suggest that, PgPIP2;6gene
can be deployed to engineer stress tolerant transgenic crops
for sustained growth and productivity under unfavourable
conditions
