problem with auto-fill-mode in gnus with org

[Eric S Fraga <e.fraga@ucl.ac.uk>]

Hello all,

I have recently started using pabbrev again.  However, I found that
using orgstruct mode within Message buffers (in gnus) caused pabbrev to
not work properly.  Not sure why (something to pursue later).

So I decided to not enable orgstruct mode.  However, by doing so, I get
the following error whenever I try to type in a line longer than my
auto-fill-column:

,----
| Debugger entered--Lisp error: (void-variable orgtbl-line-start-regexp)
|   org-adaptive-fill-function()
|   org-auto-fill-function()
|   self-insert-command(1)
|   funcall-interactively(self-insert-command 1)
|   call-interactively(self-insert-command nil nil)
|   command-execute(self-insert-command)
`----

I have

  (setq auto-fill-function 'org-auto-fill-function)

in my message-mode-hook so I do expect org to be involved in my message
composition.  Am I responsible for initialisation of org in this
context?  What am I missing?

Thanks,
eric

-- 
: Eric S Fraga (0xFFFCF67D), Emacs 25.0.50.1, Org release_8.3beta-558-g83d8a2