IMPAIRED PHOTOASSIMILATE PARTITIONING CAUSED BY PHLOEM-SPECIFIC REMOVAL OF PYROPHOSPHATE CAN BE COMPLEMENTED BY A PHLOEM-SPECIFIC CYTOSOLICYEAST-DERIVED INVERTASE IN TRANSGENIC PLANTS
J. Lerchl et al., IMPAIRED PHOTOASSIMILATE PARTITIONING CAUSED BY PHLOEM-SPECIFIC REMOVAL OF PYROPHOSPHATE CAN BE COMPLEMENTED BY A PHLOEM-SPECIFIC CYTOSOLICYEAST-DERIVED INVERTASE IN TRANSGENIC PLANTS, The Plant cell, 7(3), 1995, pp. 259-270
Constitutive expression of the Escherichia coli ppa gene encoding inor
ganic pyrophosphatase resulted in sugar accumulation in source leaves
and stunted growth of transgenic tobacco plants, The reason for this p
henotype was hypothesized to be reduced sucrose utilization and loadin
g into the phloem. To study the role of PPI in phloem cells, a chimeri
c gene was constructed using the phloem-specific rolC promoter of Agro
bacterium rhizogenes to drive the expression of the ppa gene. Removal
of cytosolic PPI in those cells resulted in photoassimilate accumulati
on in source leaves, chlorophyll loss, and reduced plant growth, From
these data, it was postulated that sucrose hydrolysis via sucrose synt
hase is essential for assimilate partitioning, To bypass the PPi-depen
dent sucrose synthase step, transgenic plants were produced that expre
ss various levels of the yeast suc2 gene, which encodes cytosolic inve
rtase, in their phloem cells, To combine the phloem-specific expressio
n of the ppa gene and the suc2 gene, crosses between invertase- and py
rophosphatase-containing transgenic plants were performed. Analysis of
their offspring revealed that invertase can complement the phenotypic
effects caused by the removal of PPI in phloem cells.