Download both root growth inhibition and medium alkalinization activities of the

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts
no text concepts found
Transcript 
BOTH ROOT GROWTH INHIBITION AND MEDIUM
ALKALINIZATION ACTIVITIES OF THE PEPTIDE
HORMONE RALF CAN BE DISSOCIATED
Ceciliato PHO 1*, Silva-Filho MC 2 and Moura DS1
Dep. de Ciências Biológicas/ Laboratório de Bioquímica de Proteínas, Escola Superior de Agricultura “Luiz de Queiroz”, Univ. de São Paulo,
Piracicaba, SP, 13418-900. 2Dep. de Genética/ Laboratório de Biologia Molecular de Plantas, Escola Superior de Agricultura “Luiz de Queiroz”,
Univ. de São Paulo, Piracicaba, SP, 13418-900.
1
*E-mail: [email protected]
Keywords: Arabidopsis thaliana, structure-activity, alkalinization assay, heterologous expression, peptide hormone.
RALF (Rapid Alkalinization Factor) is a 5kDa hormone peptide that is involved in cell elongation. There are six biological
activities well characterized for this hormone: arrest of root growth and hypocotyl elongation, increase of intracellular calcium,
induction of a MAP kinase, alkalinization of the extracellular medium and arrest of pollen tube growth. The model plant
Arabidopsis thaliana has 37 genes coding for different isoforms of this hormone. A similarity analysis revealed that only nine
of the 37 isoforms are closely related to the original RALF isolated from tobacco leaves. All of the nine isoforms inhibit root
growth and hypocotyl elongation with exception of the pollen isoform AtRALF4. The alkalinization of the extracellular medium
caused by the AtRALF4 isoform is also unique among the nine isoforms, its half-maximal activity is a 1000-fold higher than
that for the others. Based on the similarities of primary structure among the nine isoforms, a series of mutant peptides were
designed and heterologously expressed in E. coli. Our goal was the identification of amino acids determinants of the biological
activities of the peptide. The mutant AtRALF4(N92A) restores the conserved motif -ANPY- that is modified in the AtRALF4.
The AtRALF4(N92A) mutant peptide recovered the root growth inhibition activity without any changes in the alkalinization of
the extracellular medium. Another mutant, AtRALF4(R78G, R79A, R80Q), substitutes a series of basic residues present only
in the AtRALF4 by the residues present in the other isoforms. The AtRALF4(R78G, R79A, R80Q) peptide partially recovered
the alkalinization activity but no changes in the root growth inhibition activity were observed. Our results suggests that the both
biological activities of root and hypocotyl growth inhibition and alkalinization of the extracellular medium can be dissociated
by changing specific amino acids, putative determinants of the peptide activities.
Acknowledgments: FAPESP, CNPq and Pró-Reitoria de Pesquisa/ USP.
8
Related documents