Intergrative Proteomic and Transcriptomic analysis of a Male Sterile Cybrid Pummelo and Its Fertile Type Revealed Altered Gene Expression Related Cytoplasmic Male Sterility

Male sterile and seedless traits are important for citrus breeding. Citrus cybrid generated from protoplast fusion with foreign mitochondria is an ideal material for cytoplasmic male sterility (CMS) studies. Herein, we used RNA-seq based transcriptome and iTRAQ depended proteome analyses to identify differentially expressed genes (DEGs) and proteins between male sterile cybrid (G1+HBP) and its fertile type (HBP) with the aim to analyze their potential roles in floral bud and pollen development. Transcriptome data showed that DEGs mainly involved in nucleic acid binding, floral bud identification, and hormone metabolism. Especially, expression level of APETALA3 which controlled stamen primodia differentiation and development was significantly down-regulated in G1+HBP, though it was restricted to correct floral whorls that confirmed by Real-time PCR and RNA in-situ hybridization. Proteins down-regulated in G1+HBP include those involved in carbohydrate and energy metabolism, protein synthesis and degradation, and nucleotide binding. Moreover, expression levels of CYP716 and GA20ox were confirmed by Real-time PCR and Western blot, which indicated that they were significantly down-regulated at stamen development stage and closely related to male sterility in G1+HBP. On the contrary, serine protease inhibitor and aldehyde dehydrogenase (ALDH) were up-regulated in G1+HBP. Correlation analysis of transcriptome and proteome data displayed that more than half of the protein levels were different from those predicted by their mRNA levels, indicating that post-transcriptional modifications existed at stages of floral bud development. Our analyses provides a valuable inventory of genes and proteins involved in floral buds development and contribute to elucidating CMS mechanisms in the cybrid pummelo.