Comparative proteomic analysis of the maize responses to early leaf senescence induced by preventing pollination

The aim of this study was to explore the molecular mechanisms of induced leaf senescence by preventing pollination in maize using a proteomic method combined with other physiological methods. An elite maize inbred line Yu816 was selected for evaluation of its senescence mechanism. Phenotypic and chlorophyll content analysis revealed that the onset of leaf senescence occurred earlier in non-pollinated (NONPOL) leaves than pollinated (POL) leaves. Leaf protein species of NONPOL and POL leaves were separately extracted and their proteomes were assessed using isobaric tags for relative and absolute quantitation (iTRAQ) analysis. A total of 4371 protein species were identified, of which 809 exhibited differentially altered abundance (P < 0.05). The identified protein species were related to diverse functions including photosystems, plant hormones, cell death, oxidative degradation, and protein metabolism, suggesting a potential signaling cascade for ear leaf senescence induced by pollination prevention. In addition, leaf total soluble sugar and leaf starch contents were remarkably higher in NONPOL plants than in POL plants. These findings suggest that induced leaf senescence might be associated with nutrient remobilization. Our results reveal a network of molecular mechanisms at the protein level and provide some insights into the early senescence mechanism in higher plants. Biological significance: The coordination between growth and timing for senescence is critical for maize production. However, the molecular mechanism of induced leaf senescence by preventing pollination in maize remains to be further elucidated at the proteomic level. Herein, we revealed some new protein species that are involved in hormone signaling, glycometabolism, oxidation-reduction, protein degradation and photosystem breakdown, and other biological processes that were not previously known to be associated with leaf senescence. This is the first large-scale proteomics study to examine induced leaf senescence in maize by preventing pollination.