Abstract
Pollen germination, along with pollen tube growth, is an essential process for the reproduction of flowering plants. The germinating pollen with tip-growth characteristics provides an ideal model system for the study of cell growth and morphogenesis. As an essential step toward a detailed understanding of this important process, the objective of this study was to comprehensively analyze the transcriptome changes during pollen germination and pollen tube growth. Using Affymetrix Arabidopsis (Arabidopsis thaliana) ATH1 Genome Arrays, this study is, to our knowledge, the first to show the changes in the transcriptome from desiccated mature pollen grains to hydrated pollen grains and then to pollen tubes of Arabidopsis. The number of expressed genes, either for total expressed genes or for specifically expressed genes, increased significantly from desiccated mature pollen to hydrated pollen and again to growing pollen tubes, which is consistent with the finding that pollen germination and tube growth were significantly inhibited in vitro by a transcriptional inhibitor. The results of Gene Ontology analyses showed that expression of genes related to cell rescue, transcription, signal transduction, and cellular transport was significantly changed, especially for up-regulation, during pollen germination and tube growth. In particular, genes of the calmodulin/calmodulin-like protein, cation/hydrogen exchanger, and heat shock protein families showed the most significant changes during pollen germination and tube growth. These results demonstrate that the overall transcription of genes, both in the number of expressed genes and in the levels of transcription, was increased. Furthermore, the appearance of many novel transcripts during pollen germination as well as tube growth indicates that these newly expressed genes may function in this complex process.
Highlights
Pollen germination, along with pollen tube growth, is an essential process for the reproduction of flowering plants
To test whether ongoing transcription plays any role in Pollen germination (PG) and pollen tube growth (PTG), the transcription inhibitor actinomycin D (Act D) was used during the in vitro PG assays
The transitions from mature pollen grains (MP) to hydrated pollen grains (HP) and from HP to pollen tubes (PT) were regarded as PG and PTG, respectively
Summary
Along with pollen tube growth, is an essential process for the reproduction of flowering plants. As an essential step toward a detailed understanding of this important process, the objective of this study was to comprehensively analyze the transcriptome changes during pollen germination and pollen tube growth. Genes of the calmodulin/calmodulin-like protein, cation/hydrogen exchanger, and heat shock protein families showed the most significant changes during pollen germination and tube growth. These results demonstrate that the overall transcription of genes, both in the number of expressed genes and in the levels of transcription, was increased. Pollen germination (PG) and pollen tube growth (PTG) are continuous and highly polarized processes with tip-growth characteristics; they provide an ideal model system for the study of cell growth and morphogenesis in a broader sense (Feijoet al., 2001, 2004). Our results demonstrate that the overall transcription was increased along with PG and PTG, suggesting that some newly transcribed and/or transcriptionally changed genes may play roles in the regulation of PG and PTG
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