Microarray-based Analysis Of Gene Expression Profiles In The Shoot Apex Of Wheat During Vernalization

Vernalization is an important physiological process for heading date and spike initiation of winter wheat (Triticum aestivum L.). To study the molecular basis of vernalization in wheat, total RNAs were isolated from shoot apex after treatment at 4°C for 0, 5, 10, 15, 20 days for Microarray hybridization. Based on the Microarray data, 1201 differently expressed sequences were identified (FDR<1%). We examined the expression pattern of different class genes in shoot apex and leaves with or without vernalization. The results were as follows:1. Microarray data analysisThe SAM system software was used to analyze the Microarray data. When the FDR (False Discovery Rate) < 0.1, there were 1201 sets of probes passed the significant difference test. Eighty three percent ( 10/12) differently expressed sequences were confirmed by qRT-PCR. Two hundred thirty three sets of probes may be involved in the transcriptional control of genes expression in wheat shoot apex during vernalization. Classification of differently expressed genes by their functions shows that the genes involved in protein kinase, oxidordeuctase, transferase and transcriptional regulation play the important roles in the wheat vernalization process.2. Expression patterns of the genes involved in vernalization.The Microarray data displayed the primary expression patterns of the genes involved in vernalization. We further used qRT-PCR method to examine the expression patterns of these genes in shoot apex and leaves with or without vernalization treatment. The qRT-PCR results showed that the expression of VRN1 was induced in the shoot apex and leaves with vernalization treatment; but VRN1 was not expressed in the shoot apex or leaves without vernalization. VRN2 was not expressed in the shoot apices with or without vernalization; whereas VRN2 was expressed in leaves, and the vernalization treatment just represses its expression level slightly. Expression of VRN3 was not detected in both shoot apices and leaves with or without vernalization. The results supported the hypothesis that activation of VRN1 mediates the low-temperature flowering response in wheat.3. MADS-box genes may play the important roles in wheat vernalizationSince many MADS-box genes involved in the flowering control and floral development in plants, we examined the expression patterns of wheat MADS-box genes in shoot apex and leaves with or without vernalization treatment. Among them, six genes were chosen for further expression analysis. TaMADS1 and TaAGL32 displayed a similar expression pattern with VRN1 in shoot apices during vernalization or not, but they were not expressed in the leaves. Based on their expression patterns, we proposed that TaMADS1 and TaAGL32 may function together with VRN1 and WFL. TaAGL1, TaAGL11, TaAGL13 and TaAGL41 showed the reduced expression levels in shoot apices with vernalization treatment; but low expression level was detected in leaves during vernalization or not. It was suggested that they may belongs to the repressors of flowering in shoot apices.4. Histone modification and DNA methylation may be involved in the process of wheat vernalizationDuring vernalization, the levels of Histone modification and DNA methylation had been determined. Based on the microarray data, we examined the expression patterns of some genes including TaVIL1, TaVIL3, TaHAT2, TaHDAC3, TaCMT3 and TaMBD1, and these genes demonstrated the reduced expression patterns. By analysis of the expression levels of those genes in shoot apex with vernalization and without vernalization, we found that low temperature could repress the expression leves of these genes. Thus, it was proposed that these genes may participate in the regulation of gene expression during vernalization in wheat.5. The flowering time was delayed by overexpression of TaAP2 in ArabidopsisFinally, we isolate six transcription factor genes from these 233 sequences. Late flowering phenotype occurred in overexpressed TaAP2 plants under long day conditions. Related to the deduced expression pattern of TaAP2 in vernalized shoot apex, we proposed that TaAP2 may be a repressor of wheat flowering.