If you just want to extract the TAIR id, you could use this regex:

my ($tair_id) = $str2 =~ /(AT\dG\d{5})/i;
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If you want to fetch the alternative splice form suffixes as well (e.g. AT1G71260.1), you could use:

my ($tair_id) = $str2 =~ /(AT\dG\d{5}(?:\.\d+)?)/i;
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