The low phytic acid1-241 (lpa1-241) maize mutation altersthe accumulation of anthocyanin pigment in the kernel

The lpa1 mutations in maize are caused by
lesions in the ZmMRP4 (multidrug resistance-associated
proteins 4) gene. In previous studies, several mutations have been isolated in this locus causing a reduction of phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphosphate, or InsP6) content and an
equivalent increasing of free phosphate. In particular, the
lpa1-241 mutation causes a reduction of up to 90% of
phytic acid, associated with strong pleiotropic effects on
the whole plant. In this work, we show, for the first time to
our knowledge, an interaction between the accumulation of
anthocyanin pigments in the kernel and the lpa mutations.
In fact the lpa1-241 mutant accumulates a higher level of
anthocyanins as compared to wild type either in the embryo
(about 3.8-fold) or in the aleurone layer (about 0.3-fold) in
a genotype able to accumulate anthocyanin. Furthermore,
we demonstrate that these pigments are mislocalised in
the cytoplasm, conferring a blue pigmentation of the
scutellum, because of the neutral/basic pH of this cellular
compartment. As a matter of fact, the propionate treatment,
causing a specific acidification of the cytoplasm, restored
the red pigmentation of the scutellum in the mutant and
expression analysis showed a reduction of ZmMRP3
anthocyanins’ transporter gene expression. On the whole,
these data strongly suggest a possible interaction between
the lpa mutation and anthocyanin accumulation and compartmentalisation in the kernel.