The Absence of Heat Shock
Protein HSP101 Affects the
Proteome of Mature and Germinating Maize Embryos
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Abstract
Maize heat shock protein HSP101 accumulates during embryo
maturation
and desiccation and persists at high levels during the first 24 h
following kernel imbibition in the absence of heat stress. This protein
has a known function in disaggregation of high molecular weight complexes
and has been proposed to be a translational regulator of specific
mRNAs. Here, a global proteomic approach was used to identify changes
in the maize proteome due to the absence of HSP101 in embryos from
mature-dry or 24 h-imbibed kernels. A total of 26 protein spots from
the mature dry embryo exhibited statistically significant expression
changes in the L10 inbred <i>hsp101</i> mutant (<i>hsp101-m5::Mu1</i>/<i>hsp101-m5::Mu1</i>) line as
compared to the corresponding wild type (<i>Hsp101</i>/<i>Hsp101</i>). Additional six spots reproducibly showed qualitative
changes between the mutant and wild-type mature and germinating embryos.
Several chaperones, translation-related proteins, actin, and enzymes
participating in cytokinin metabolism were identified in these spots
by tandem mass-spectrometry (MS). The proteomic changes partially
explain the altered root growth and architecture observed in young <i>hsp101</i> mutant seedlings. In addition, specific protein de
novo synthesis was altered in the 24 h-imbibed mutant embryos indicating
that maize HSP101 functions as both chaperone and translational regulator
during germination. Supporting this, HSP101 was found as part of Cap-binding
and translation initiation complexes during early kernel imbibition.
Overall, these findings expose the relevance of maize HSP101 for protein
synthesis and balance mechanisms during germination