AUTHOR=Sagor G.H.M. , Chawla Pratima , Kim Dong Wook , Berberich Thomas , Kojima Seiji , Niitsu Masaru , Kusano Tomonobu 

TITLE=The polyamine spermine induces the unfolded protein response via the MAPK cascade in Arabidopsis

JOURNAL=Frontiers in Plant Science

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2015.00687

DOI=10.3389/fpls.2015.00687

ISSN=1664-462X

ABSTRACT=<p>In <italic>Arabidopsis</italic> three basic region leucine zipper (bZIP) transcription factor genes, <italic>bZIP17</italic>, <italic>bZIP28</italic>, and <italic>bZIP60</italic>, play crucial roles in the unfolded protein response (UPR). Previously we found that <italic>bZIP60</italic> is one of the spermine-induced genes. Consequently we further investigated the response of all the three bZIP genes to spermine. Expression of <italic>bZIP17</italic>, <italic>bZIP28</italic>, and <italic>bZIP60</italic>, and also their target genes was activated by spermine application as well as in plants with elevated endogenous spermine levels. Furthermore, spermine activated the splicing of the <italic>bZIP60</italic> transcript mediated by the ribonuclease activity of inositol-requiring enzyme 1 and also recruited bZIP17 and bZIP60 proteins from endoplasmic reticulum to nucleus. We therefore propose that spermine is a novel UPR inducer. Moreover, induction of UPR by spermine required calcium-influx to the cytoplasm and the genes for mitogen-activated protein kinase kinase 9 (<italic>MKK9</italic>), mitogen-activated protein kinase 3 (<italic>MPK3</italic>) and <italic>MPK6</italic>. The result indicates that spermine-induced UPR is mediated by the MKK9-MPK3/MPK6 cascade in <italic>Arabidopsis</italic>.</p>