Comparative Proteomics Reveals a Role for Seed Storage Protein AmA1 in Cellular Growth, Development, and Nutrient Accumulation

Seed storage proteins are known to
be utilized as carbon and nitrogen
source for growing seedlings and thus are considered as potential
candidates for nutritional improvement. However, their precise function
remains unknown. We have earlier shown that ectopic expression of
a seed storage protein, AmA1, leads to increase in protein besides
high tuber yield in potato. To elucidate the AmA1-regulated molecular
mechanism affecting increased protein synthesis, reserve accumulation,
and enhanced growth, a comparative proteomics approach has been applied
to tuber life-cycle between wild-type and AmA1 potato. The differential
display of proteomes revealed 150 AmA1-responsive protein spots (ARPs)
that change their intensities more than 2.5-fold. The LC–ESI-MS/MS
analyses led to the identification of 80 ARPs presumably associated
with cell differentiation, regulating diverse functions, viz., protein
biogenesis and storage, bioenergy and metabolism, and cell signaling.
Metabolome study indicated up-regulation of amino acids paralleling
the proteomics analysis. To validate this, we focused our attention
on anatomical study that showed differences in cell size in the cortex,
premedullary zone and pith of the tuber, coinciding with AmA1 expression
and localization. Further, we interrogated the proteome data using
one-way analysis of variance, cluster, and partial correlation analysis
that identified two significant protein modules and six small correlation
groups centered around isoforms of cysteine protease inhibitor, actin,
heat shock cognate protein 83 and 14-3-3, pointing toward AmA1-regulated
overlapping processes of protein enhancement and cell growth perhaps
through a common mechanism of function. A model network was constructed
using the protein data sets, which aim to show how target proteins
might work in coordinated fashion and attribute to increased protein
synthesis and storage reserve accumulation in AmA1 tubers on one hand
and organ development on the other.