In Meristematic zone, 

cells divide both in the direction of the root base to form cells that will differentiate into the tissues of the functional root and in the direction of the root apex to form the root cap

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Within the nucleus, R-Smads are modified by:

Phosphorylation of linker domains

Acetylation of MH1 domains

Dephosphorylation of the C-terminal serines by nuclear

phosphatases

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BMP proteins, activate a different set of receptors that are similar to the TGF-β RI and RII proteins but phosphorylate other R-Smads, Smad1, Smad5, & Smad8

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Smad4 was originally called DPC (deleted in pancreatic cancer)

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Negative regulators of TGF-β signaling are induced by TGF-β signaling (Example of Negative feedback): 

Ski 

SnoN 

I-Smads (Smad7)

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SnoN and Ski trigger abnormal cell proliferation by blocking the Smad-complex.

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