Abstract
Mature pollen from most plant species is metabolically quiescent; however, after pollination, it germinates quickly and gives rise to a pollen tube to transport sperms into the embryo sac. Because methods for collecting a large amount of in vitro germinated pollen grains for transcriptomics and proteomics studies from model plants of Arabidopsis and rice are not available, molecular information about the germination developmental process is lacking. Here we describe a method for obtaining a large quantity of in vitro germinating rice pollen for proteomics study. Two-dimensional electrophoresis of approximately 2300 protein spots revealed 186 that were differentially expressed in mature and germinated pollen. Most showed a changed level of expression, and only 66 appeared to be specific to developmental stages. Furthermore 160 differentially expressed protein spots were identified on mass spectrometry to match 120 diverse protein species. These proteins involve different cellular and metabolic processes with obvious functional skew toward wall metabolism, protein synthesis and degradation, cytoskeleton dynamics, and carbohydrate/energy metabolism. Wall metabolism-related proteins are prominently featured in the differentially expressed proteins and the pollen proteome as compared with rice sporophytic proteomes. Our study also revealed multiple isoforms and differential expression patterns between isoforms of a protein. These results provide novel insights into pollen function specialization.
Highlights
Mature pollen from most plant species is metabolically quiescent; after pollination, it germinates quickly and gives rise to a pollen tube to transport sperms into the embryo sac
Our preliminary experiments showed that most Mature Rice Pollen Grains (MPGs) of rice became inviable when stored for more than 10 min at room temperature or Ϫ80 °C
Anther debris were removed by filtering the culture, and germinated rice pollen grains (GPGs) were collected by centrifugation
Summary
Mature pollen from most plant species is metabolically quiescent; after pollination, it germinates quickly and gives rise to a pollen tube to transport sperms into the embryo sac. 160 differentially expressed protein spots were identified on mass spectrometry to match 120 diverse protein species These proteins involve different cellular and metabolic processes with obvious functional skew toward wall metabolism, protein synthesis and degradation, cytoskeleton dynamics, and carbohydrate/energy metabolism. The observation suggests that the transcriptional characteristics involve pollen function specialization These studies determined that pollen transcriptome has a functional skew toward transcripts implicated in cell wall metabolism, signaling, and cytoskeletal dynamics. These results support the early notion that mature pollen has stored presynthesized mRNAs [11] and present a novel insight into pollen function specialization at the whole genome level. Given the ability of pollen to initiate protein synthesis rapidly upon germination and the carbon skeleton/energy needs for active
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