Yes the databases are still not well designed smartly to do this job or the information for very recently sequenced genome like Triticum aestivum  and not Triticum Aestivum is unavailable.

COG database likely could be useful?

alternative, searching the Arabidopsis database to get the top homolog, and then use this homolog as query search Ta base. if the top record is that query item you search At base, they two might be orthology.

Thank you dear Shan LIang.

This is for one gene, but I have a gene list of a family.

You can seach for orthologous in Ensembl Plant:  http://plants.ensembl.org/index.html

 I've used it, very nice tool.

Good Luck

How can i import my gene list to the http://plants.ensembl.org/index.html web site?

@Kaushal, I think  we use the BLAST just for a gene not for a gene list.