This provides a template based on the official PNAS LaTeX template (for Overleaf, pnas-new.cls).

A few notes:

• The LaTeX template uses quite a few custom fields, for the most part these have been turned into yaml header sections (e.g. abstract, author contributions, acknowledgements, etc). Perhaps there is a way to do this that doesn't clutter the yaml header with so much text.
• pandoc introduces a dependency on longtable when turning markdown tables into LaTeX. longtable is incompatible with any two-column style, including this one. See longtable not compatible with 2-column LaTeX documents jgm/pandoc#1023. Users can thus not create markdown tables, though can of course use knitr utilities to generate the desired LaTeX table directly anyway, so hopefully this is not an issue. (It appears that longtable is also not always included in other templates here, which could create similar problems for users writing markdown tables.
• The template download includes several custom .sty files. Additionally I have included some .sty files needed here that are not readily found in a tex build that is otherwise sufficient to compile R packages and the default pandoc templates (i.e. the hadleyverse docker image). I've put these in skeleton dir, I'm sometimes unclear what goes in skeleton and what goes in resources. Feedback on that or anything else is welcome, will help me write these faster.
• I added a test following the existing pattern.