The Arabidopsis polyamine transporter LHR1/PUT3 modulates heat responsive gene expression by enhancing mRNA stability

Abstract

Polyamines involve in gene regulation by interacting with and modulating the functions of various anionic macromolecules such as DNA, RNA and proteins. In this study, we identified an important function of the polyamine transporter LHR1 (LOWER EXPRESSION OF HEAT RESPONSIVE GENE1) in heat-inducible gene expression in Arabidopsis thaliana. The lhr1 mutant was isolated through a forward genetic screening for altered expression of the luciferase reporter gene driven by the promoter from the heat-inducible gene AtHSP18.2. The lhr1 mutant showed reduced induction of the luciferase gene in response to heat stress and was more sensitive to high temperature than the wild type. Map-based cloning identified that the LHR1 gene encodes the polyamine transporter PUT3 (POLYAMINE UPTAKE TRANSPORTER 3) localized in the plasma membrane. The LHR1/PUT3 is required for the uptake of extracellular polyamines and plays an important role in stabilizing the mRNAs of several crucial heat stress responsive genes under high temperature. Genome-wide gene expression analysis using RNA-seq identified an array of differentially expressed genes, among which the transcript levels of some of the heat shock protein genes significantly reduced in response to prolonged heat stress in the lhr1 mutant. Our findings revealed an important heat stress response and tolerance mechanism involving polyamine influx which modulates mRNA stability of heat-inducible genes under heat stress conditions.

The plasma‐membrane polyamine transporter PUT3 is regulated by the Na+/H+ antiporter SOS1 and protein kinase SOS2

“…We propose that under heat stress, SOS2 is activated by an as yet to be identified mechanism, and PUT3, SOS1 and SOS2 form a complex; SOS2 phosphorylates PUT3 and enhances PUT3 transport activity, which increases the cytosolic concentration of PAs. The accumulated PAs in the cytosol could function as anti‐ROS molecules to reduce oxidative stress as well as protecting molecules to stabilize cellular components such as mRNAs, as we have shown previously (Shen et al ., ). By forming this complex under heat stress, the activity of SOS1 could also be enhanced, and increased SOS1 activity could create a microenvironment of H + gradient that favors the PUT3 transporter.…”

“…The PUT3OE transgenic line (Shen et al, 2016), sos1 (Shi et al, 2000), sos2 (Liu et al, 2000) and Col-0 wild type were used in this study. The PUT3OE transgenic line was crossed with sos1-1 and sos2-2, respectively, and the homozygous lines were identified in the F 3 generation (Supporting Information Fig.…”

“…Previous studies have identified several Arabidopsis mutants showing resistance to PQ, including sos1 , sos2 and put3 (Katiyar‐Agarwal et al ., ; Chung et al ., ; Shen et al ., , Chai et al ., ). We thus reasoned that these three genes may function in the same pathway to modulate PQ resistance.…”

“…LAT3/PUT1, LAT4/PUT2 and LAT1/PUT3 display high sequence similarity to each other (68-76%) and exhibit polyamine transport activity (Fujita & Shinozaki, 2014). PUT3 is localized in the plasma membrane with 12 predicted transmembrane domains and cytoplasmic N-and C-terminal tails (Fujita et al, 2012, Shen et al, 2016. PUT3 was first reported to transport PAs as well as their structural analog paraquat (PQ) into the plant cells (Fujita et al, 2012), and was later found to be involved in mediating the longdistance transport of both PAs and thiamine (vitamin B1) in the phloem from shoot to root (Martinis et al, 2016).…”

“…Under heat stress, PUT3 is responsible for maintaining the stability of the mRNAs of several heat-responsive genes. Exogenous application of spermine reduces the degradation of heat-induced transcripts with a relatively short half-life, such as those from HSFA2, HSP101 and HSP70, but has little effect on transcripts with a relatively long half-life (Shen et al, 2016). Despite its important role in PA homeostasis and heat stress response, the regulation of transport activity of PUT3 is largely unknown.…”