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Medientyp:
E-Artikel
Titel:
Spatio-temporal sequence of cross-regulatory events in root meristem growth
Beteiligte:
Scacchi, Emanuele;
Salinas, Paula;
Gujas, Bojan;
Santuari, Luca;
Krogan, Naden;
Ragni, Laura;
Berleth, Thomas;
Hardtke, Christian S.
Erschienen:
Proceedings of the National Academy of Sciences, 2010
Erschienen in:
Proceedings of the National Academy of Sciences, 107 (2010) 52, Seite 22734-22739
Sprache:
Englisch
DOI:
10.1073/pnas.1014716108
ISSN:
0027-8424;
1091-6490
Entstehung:
Anmerkungen:
Beschreibung:
<jats:p>
A central question in developmental biology is how multicellular organisms coordinate cell division and differentiation to determine organ size. In Arabidopsis roots, this balance is controlled by cytokinin-induced expression of
<jats:italic>SHORT HYPOCOTYL 2</jats:italic>
(
<jats:italic>SHY2</jats:italic>
) in the so-called transition zone of the meristem, where SHY2 negatively regulates auxin response factors (ARFs) by protein–protein interaction. The resulting down-regulation of
<jats:italic>PIN-FORMED</jats:italic>
(
<jats:italic>PIN</jats:italic>
) auxin efflux carriers is considered the key event in promoting differentiation of meristematic cells. Here we show that this regulation involves additional, intermediary factors and is spatio-temporally constrained. We found that the described cytokinin–auxin crosstalk antagonizes
<jats:italic>BREVIS RADIX</jats:italic>
(
<jats:italic>BRX</jats:italic>
) activity in the developing protophloem.
<jats:italic>BRX</jats:italic>
is an auxin-responsive target of the prototypical ARF MONOPTEROS (MP), a key promoter of vascular development, and transiently enhances
<jats:italic>PIN3</jats:italic>
expression to promote meristem growth in young roots. At later stages, cytokinin induction of
<jats:italic>SHY2</jats:italic>
in the vascular transition zone restricts
<jats:italic>BRX</jats:italic>
expression to down-regulate
<jats:italic>PIN3</jats:italic>
and thus limit meristem growth. Interestingly, proper
<jats:italic>SHY2</jats:italic>
expression requires
<jats:italic>BRX</jats:italic>
, which could reflect feedback on the auxin responsiveness of
<jats:italic>SHY2</jats:italic>
because BRX protein can directly interact with MP, likely acting as a cofactor. Thus, cross-regulatory antagonism between
<jats:italic>BRX</jats:italic>
and
<jats:italic>SHY2</jats:italic>
could determine ARF activity in the protophloem. Our data suggest a model in which the regulatory interactions favor
<jats:italic>BRX</jats:italic>
expression in the early proximal meristem and
<jats:italic>SHY2</jats:italic>
prevails because of supplementary cytokinin induction in the later distal meristem. The complex equilibrium of this regulatory module might represent a universal switch in the transition toward differentiation in various developmental contexts.
</jats:p>