Contribution of Proteomics in the Identification of Novel Proteins Associated with Plant Growth

The epidermis is not only the interphase
between the plant and
the environment but also a growth-limiting tissue. Understanding the
initiation and regulation of its expansion growth is essential for
addressing the need for more food and fuel. We used mass spectrometry
to identify proteins from auxin (indole-3-acetic acid; IAA)-induced
rapidly growing corn (Zea mays) coleoptiles to find
possible candidates controlling this growth as well as the underlying
cell wall and cuticle biosynthesis. Excised sections were incubated
for 4 h in the absence or presence of IAA, protein extracted, and
analyzed using LC-ESI-MS/MS. Of 86 proteins identified, 15 showed
a predicted association with cell wall/cuticle biosynthesis or trafficking
machinery; four identifications revealed novel proteins of unknown
function. In parallel, real-time PCR indicated that the steady-state
mRNA levels of genes with a known or predicted role in cell-wall biosynthesis
increase upon treatment with auxin. Importantly, genes encoding two
of the hypothetical proteins also show higher levels of mRNA; additionally,
their gene expression is down-regulated as coleoptile growth ceases
and up-regulated in expanding leaves. This suggests a major role of
those novel proteins in the regulation of processes related to cell
and organ expansion and thus plant growth.