Abstract
Plasma membrane intrinsic proteins (PIPs), which function as water channels in plant cells, can be divided into 2 subgroups, PIP1 and PIP2. We had found that barley (Hordeum vulgare) PIP1s except for HvPIP1;3 show little water transport activity when expressed alone in Xenopus laevis oocytes, but significantly enhance the water transport activity of HvPIP2 when co-expressed in oocytes most likely via heteromerization of HvPIP1 and HvPIP2.
An amino acid sequence alignment of all HvPIP1 highlighted 2 amino acids in the vicinity of the N-terminal, conserved in all HvPIP1s but HvPIP1;3. Each single and double point-mutated HvPIP1;3 showed significant enhancement of the water transport activity of HvPIP2;1 when co-expressed in oocytes in sharp contrast to the case of co-expression of wildtype HvPIP1;3 and HvPIP2;1. The effect of inverse point mutations on the corresponding amino acids of HvPIP1;2 and HvPIP1;4 will be examined and the molecular mechanism of heteromerization of HvPIP1 and HvPIP2 will be discussed.
