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Thermospermine levels are controlled by an auxin‐dependent feedback loop mechanism in Populus xylem
Author(s) -
Milhinhos Ana,
Prestele Jakob,
Bollhöner Benjamin,
Matos Andreia,
VeraSirera Francisco,
Rambla José L.,
Ljung Karin,
Carbonell Juan,
Blázquez Miguel A.,
Tuominen Hannele,
Miguel Célia M.
Publication year - 2013
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.12231
Subject(s) - xylem , auxin , microbiology and biotechnology , biology , transcription factor , biochemistry , leucine zipper , polyamine , negative feedback , indole 3 acetic acid , endogeny , gene expression , botany , gene , physics , quantum mechanics , voltage
Summary Polyamines are small polycationic amines that are widespread in living organisms. Thermospermine, synthesized by thermospermine synthase ACAULIS 5 ( ACL 5), was recently shown to be an endogenous plant polyamine. Thermospermine is critical for proper vascular development and xylem cell specification, but it is not known how thermospermine homeostasis is controlled in the xylem. We present data in the Populus model system supporting the existence of a negative feedback control of thermospermine levels in stem xylem tissues, the main site of thermospermine biosynthesis. While over‐expression of the ACL 5 homologue in Populus , POPACAULIS 5 , resulted in strong up‐regulation of ACL 5 expression and thermospermine accumulation in leaves, the corresponding levels in the secondary xylem tissues of the stem were similar or lower than those in the wild‐type. POPACAULIS 5 over‐expression had a negative effect on accumulation of indole‐3‐acetic acid, while exogenous auxin had a positive effect on POPACAULIS 5 expression, thus promoting thermospermine accumulation. Further, over‐expression of POPACAULIS 5 negatively affected expression of the class III homeodomain leucine zipper ( HD ‐Zip III ) transcription factor gene Ptt HB 8 , a homologue of At HB 8 , while up‐regulation of Ptt HB 8 positively affected POPACAULIS 5 expression. These results indicate that excessive accumulation of thermospermine is prevented by a negative feedback control of POPACAULIS 5 transcript levels through suppression of indole‐3‐acetic acid levels, and that Ptt HB 8 is involved in the control of POPACAULIS 5 expression. We propose that this negative feedback loop functions to maintain steady‐state levels of thermospermine, which is required for proper xylem development, and that it is dependent on the presence of high concentrations of endogenous indole‐3‐acetic acid, such as those present in the secondary xylem tissues.