Generally, the seeds can be put in the refrigerator, which can prolong the life of the seeds through low temperature and maintain a good germination rate. Generally speaking, herbaceous flowers or vegetable seeds can be refrigerated for about 3 to 5 years in the refrigerator.

An article from ABRC (Arabidopsis Biological Resource Center) (https://abrc.osu.edu/researchers/seed) provides some info.

Article: https://abrc.osu.edu/uploads/tinymce_asset/file/63/Rivero_et_al_2014.pdf

• Seeds left at room temperature and ambient relative humidity lose viability within approximately 2 years. Seed stored dry at 4 ºC or −20 ºC should last decades.
• Below are three storage options for safe seed preservation:

1. For active collections which are accessed often, store seeds at 4 °C and 20–30 % relative humidity. Control of humidity is typically achieved by a dehumidifi cation system in the cold room. (Note that the control of relative humidity provides a safety factor in case seed containers are not sealed properly.)

2. For long-term or archival storage, the recommended temperature is subzero, preferably −20 °C and also preferably 20 % relative humidity.

3. For open containers such as envelopes, seeds can be stored at 15–16 °C, with a relative humidity maintained very carefully at 15 %. Under this controlled environment, seeds will maintain suitable low moisture content [ 16]. Storing seeds at relative humidity

I have seen colleagues storing Arabidopsis seeds in the refrigerator for years and years and they remain viable, so storing at -20ºC is a good long-term strategy.

yes -20°C is a good long term storage conditions for A thal seeds

Thanks everyone for useful advice