The Arabidopsis aminopeptidase-P (AtAPP1) is a regulator of auxin signaling.

Srinivas Nagaraj Makam, Purdue University

Abstract

Arabidopsis APP1 is a membrane-associated soluble aminopeptidase with activity against N-terminal Arg>Lys>Leu=Pro>Tyr residues. APP1 is a single copy gene and was originally isolated by its weak affinity for the auxin transport inhibitor 1-Naphthylphthalamic acid (NPA). A role in wounding responses was suggested when AtAPP1 was co-purified with proline rich proteins (PRPs) and arabinogalactan protein (AGPs) that accumulate in the cell wall in response to physical damage (Fowler et al., 1999; Murphy et al., 2002) and with the recent findings that excess use of Alanap (NPA) leading to a weakened defense response and susceptibility resulting in mature watermelon vine decline (MWVD) (Makam et al., 2005). AtAPP1 enzymatic activity is inhibited by bestatin, apstatin (a APP specific inhibitor), but activated by NPA consistent with its isolation. AtAPP1 also exhibits sensitivity to metal chelators (EDTA, EGTA) and to both leucine aminopeptidase and serine protease inhibitors. Enzyme kinetic analysis suggest an allosteric catalytic mechanisms for AtAPP1. A very unique character of AtAPP1 is its PPlase activity. This activity is involved in isomerization of cis to trans forms of prolyl residue, which is the rate limiting step for processing of proline residues in biologically important peptides. APP1 expression is induced by auxin, wounding, and jasmonic acid. APP1 exhibits affinity for WPP peptide motifs and binds poly-arg containing dynorphin A like motifs with relatively high affinity in vivo and in vitro. Mutations in such conserved di-prolyl motif stabilizes the AUX/IAAs which are central to auxin signal transduction. Events leading to such stability and factors involved in this process is still unknown. In addition, AtAPP1 has the auxin responsive TGTCTC element in its promoter and the affinity to these motifs (di-prolyl and poly-arg) suggest a crucial role for AtAPP1 in auxin responses. Results are presented here illustrating AtPP1 modulation of auxin responses through its enzymatic, mutational and interaction analysis.

Degree

Ph.D.

Advisors

Murphy, Purdue University.

Subject Area

Agronomy|Biochemistry

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