Downregulation of high-affinity potassium and sodium symporter gene,
EcHKT1;1, in Eucalyptus roots enhances salt tolerance
Abstract
Engineering for restricted root Na+ uptake could potentially enhance
salt tolerance in Eucalyptus. High-affinity K+ transporters (HKTs) have
been implicated in Na+ uptake from the external medium as in the case of
TaHKT2;1 or in the unloading of Na+ from xylem like in AtHKT1;1. To
rapidly determine the in planta role of EcHKT1:1, composite transgenics
in which EcHKT1:1 was specifically downregulated via RNAi in the roots
were generated. Compared to the controls that failed to survive at 350
mM NaCl, 33 % of the composite transgenic plantlets generated using the
EcHKT1;1 silencing construct were able to tolerate up to 400 mM NaCl. In
these composite transgenics, EcHKT1;1 downregulation ranged from 37 %
to 74 %. The average shoot to root ratio of sodium was 4.9 folds lower
than the controls indicating restricted translocation of Na+ to the
shoots. Relative expression analysis in the leaves of two non-transgenic
genotypes contrasting for their salt tolerance also showed downregulated
EcHKT1;1 expression in the tolerant clone. The study thus determined
that EcHKT1;1 is a major gene determining Na+ transport from the roots
to shoots. This study also demonstrated the utility of the composite
transgenic approach for screening genes conferring salt tolerance in
tree species.