Targeting the promoter is risky as you will still have the actual gene present. I would go for target sites in the gene itself, try for a very large deletion. Some key considerations

make sure your target sites are unique

if possible get target sites that are not in the same reading frame (or you have a higher chance of a in-frame deletion)

use the gene sequence for your ecotype of Arabidopsis for your target site selection and gRNA design

Hope this helps!

ok, you asked this question a little while ago and now have reworded it. Is for a research project and not classwork for school?

Note that a deletion (one that changes the reading frame) at the start of the coding sequence will disrupt both domains as the peptide encoded will no longer be a match to the original protein.