How is novel gene is named?

[saraelesawe]

I need someone help me to answer of this question, How is gene named?
For example: OsNAC5, OsNAC6, OsNAC7 are genes, the letters of (o) and (s) are the first letters of Oriza sativa, NAC is abbreviation of NAC protein, but what are the numbers of (5) or (6) or (7) mean?

[JackBean]

the numbers mean orthologs, i.e. there are at least 7 NAC proteins in rice genome and they were numbered as they were discovered.
(or they could be number in accordance to paralogs in other plant, e.g. Arabidopsis)

[saraelesawe]

Thank you very much for helping