I'm currently writting my thesis, where are exposed unpublished results that I would like to publish (may be after my PhD defense). Can I directly re-use text from my thesis ?
A finished thesis is a publication so any studies it includes will technically be published when you have successfully submitted your thesis. Finished theses are typically placed in university libraries and digital institutional archives and indexed in scholarly research search engines like ProQuest.
That said, there is broad recognition that theses are special kinds of publications and work is often included in a thesis despite having been published elsewhere or may be published after the thesis.
There are two major concerns:
The first is about copyright. At many universities, a thesis reflecting work does as a funded research assistant will be owned by the university. This may prevent signing a copyright agreement with a journal or publisher.
The second issue is around what you call "auto-plagiarism" and which is often called "self-plagiarism" which is a complex and controversial term used to describe attempts to inappropriately get credit for publishing the same material multiple times.
The two issues are related by distinct. Although both must be negotiated, neither will necessarily prevent you from publishing material in your thesis as an article after the thesis is done. They likely will constrain how you go about doing so.
In terms of copyright, this page by the MIT libraries about theses and copyright will give you a sense of how to negotiate the situation. It's complicated and may involve asking your university or a journal publisher for special permission.
In terms of self-plagiarism, your best bet is to be completely forthcoming at all stages. Explain in the text of your articles that the work in the article was adapted from material in your thesis. Provide a citation! Mention this fact in your coverletter to any journal.
Do research first into publishers policies in this regard before you submit. Although the large majority of publishers will publish material previously included in a thesis, there are a small number that will not. This page by the MIT libraries documents the arrangements with a couple dozen big publishers in science and engineering. Many publishers include this information on their websites and in their Frequent Asked Questions documents. Contact a librarian at your university or send an inquiry to a publisher if you have any questions.
It would be better to cite your thesis as you would another work. You can list it in the bibliography as you would any other work, but mark it (unpublished). This is similar to citing the unpublished work of other people, and marking it as (private communication) just to make it clear.
Of course, if your thesis is in (will be in) some publicly visible repository, then clearly you should cite it there.
On the other hand, if you don't intend to publish your thesis, then the work you derive from it are original/first works and you could, in theory, treat the thesis as a draft, in which case citation isn't really needed. But it could give the wrong impression if someone finds the thesis somewhere, such as a library repository.
Note that the reason for avoiding self plagiarism is to let a future reader visit the complete context of a work. Simply reusing, rather than citing, your own words short circuits this.