iTRAQ-Based Quantitative Proteomics Analysis Revealed Alterations of Carbohydrate Metabolism Pathways and Mitochondrial Proteins in a Male Sterile Cybrid Pummelo

Comprehensive
and quantitative proteomic information on citrus
floral bud is significant for understanding male sterility of the
cybrid pummelo (G1+HBP) with nuclear genome of HBP and foreign mitochondrial
genome of G1. Scanning electron microscopy and transmission electron
microscopy analyses of the anthers showed that the development of
pollen wall in G1+HBP was severely defective with a lack of exine
and sporopollenin formation. Proteomic analysis was used to identify
the differentially expressed proteins between male sterile G1+HBP
and fertile type (HBP) with the aim to clarify their potential roles
in anther development and male sterility. On the basis of iTRAQ quantitative
proteomics, we identified 2235 high-confidence protein groups, 666
of which showed differentially expressed profiles in one or more stages.
Proteins up- or down-regulated in G1+HBP were mainly involved in carbohydrate
and energy metabolism (e.g., pyruvate dehydrogenase, isocitrate dehydrogenase,
ATP synthase, and malate dehydrogenase), nucleotide binding (RNA-binding
proteins), protein synthesis and degradation (e.g., ribosome proteins
and proteasome subunits). Additionally, the proteins located in mitochondria
also showed changed expression patterns. These findings provide a
valuable inventory of proteins involved in floral bud development
and contribute to elucidate the mechanism of cytoplasmic male sterility
in the cybrid pummelo.