Abstract: Male sterility is one of the major characteristics to be used in heterosis utilization of crops, in which thermo-sensitive or photo-sensitive male sterility is very important for two-line hybridization due to the conversion of their male fertility under special weather conditions. YS type thermo-sensitive male sterile wheat (Triticum astivum L.) lines are applicable for heterosis use in the major wheat production areas of northern China. To investigate the molecular basis of male fertility conversion of YS type thermo-sensitive male sterile wheat lines, we constructed the sterile and fertile suppression subtractive hybridization (SSH) cDNA libraries respectively, using the cDNA of the male sterile or fertile young spikes from the same individual of one YS type thermo-sensitive male sterile wheat line A3017 under controlled male sterile or fertile conditions. Comparing the EST sequences between the two cDNA libraries, an EST (GenBank accession number: 36925702) highly similar to MADS box transcription factor gene was selected from the sterile SSH-cDNA library and used as the probe to search the dbEST. A pair of primers was designed based on the aligned sequence of highly homological EST sequences, and used to detect the expression difference of this gene between male sterile and fertile spikes via Reverse Transcriptase PCR (RT-PCR). The results showed that the expression of this gene in male sterile spikes was much higher than that in fertile spikes. Then the RT-PCR fragment amplified from the male sterile spikes was cloned and sequenced, a cDNA sequence with 666 bp and encoding 160 amino acids was obtained. The cDNA fragment contained the typical K-box domain of MADS-box, and designated as TaMS-MADSbox. The deduced amino acids were 94% similar to WAG (BAC22939), an MADS box transcription factor of wheat. The expression profiles of this MADS-box transcription factor gene in the male-sterile lines and their maintainers of three types of male sterile wheat lines were further analyzed via semi-quantitative RT-PCR. The result showed similar patterns that the expression of the MADS-box transcription factor gene in male-sterile lines was much higher than that in maintainers. It suggests that the expression of TaMS-MADSbox is related to the fertility conversion of male-sterile lines. The spikes are male-sterile under high-level expression of TaMS-MADSbox, while fertile under the low-level expression.

Key words: Common wheat, Thermo-sensitive male-sterility, Fertility conversion, MADS-box transcription factor, Gene expression analysis