Effect of Thermospermine on the Growth and Expression of Polyamine-Related Genes in Rice Seedlings.

Minaho Miyamoto,Taku Takahashi,Wurina Tong,Hiroyasu Motose,Satoshi Shimao

doi:10.3390/plants8080269

Abstract

A mutant defective in the biosynthesis of thermospermine, acaulis5 (acl5), shows a dwarf phenotype with excess xylem vessels in Arabidopsis thaliana. Exogenous supply of thermospermine remarkably represses xylem differentiation in the root of seedlings, indicating the role of thermospermine in proper repression of xylem differentiation. However, the effect of thermospermine has rarely been investigated in other plant species. In this paper, we examined its effect on the growth and gene expression in rice seedlings. When grown with thermospermine, rice seedlings had no clearly enlarged metaxylem vessels in the root. Expression of OsACL5 was reduced in response to thermospermine, suggesting a negative feedback control of thermospermine biosynthesis like in Arabidopsis. Unlike Arabidopsis, however, rice showed up-regulation of phloem-expressed genes, OsHB5 and OsYSL16, by one-day treatment with thermospermine. Furthermore, expression of OsPAO2 and OsPAO6, encoding extracellular polyamine oxidase whose orthologs are not present in Arabidopsis, was induced by both thermospermine and spermine. These results suggest that thermospermine affects the expression of a subset of genes in rice different from those affected in Arabidopsis.

Highlights

Thermospermine synthase is encoded by the ACAULIS5 (ACL5) gene in Arabidopsis thaliana [1]and its loss-of-function mutant acl5 shows a stunted growth along with excess xylem vessels [2,3,4,5].The point-mutated acl5 mRNA level is increased in acl5 but is reduced by exogenous thermospermine [6], suggesting a negative feedback control of thermospermine biosynthesis
This study provides an initial investigation of physiological and molecular effects of exogenous of metaxylem vessels and expression of OsACL5 in the root, suggesting its functional conservation thermospermine in rice seedlings
We confirmed that thermospermine represses both development between eudicots and monocots

Summary

Introduction

Thermospermine synthase is encoded by the ACAULIS5 (ACL5) gene in Arabidopsis thaliana [1]and its loss-of-function mutant acl shows a stunted growth along with excess xylem vessels [2,3,4,5].The point-mutated acl mRNA level is increased in acl but is reduced by exogenous thermospermine [6], suggesting a negative feedback control of thermospermine biosynthesis. Because SAC51 and SACL3 in turn compete with TMO5 or T5L1 to heterodimerize with LHW [11,13], thermospermine appears to be a part of the negative feedback regulation of auxin-induced xylem formation and thermospermine biosynthesis [14,15,16]. These results have been obtained solely from studies in Arabidopsis and, except for a study that reported on the negative feedback regulation of thermospermine homeostasis in poplar xylem tissues [17] and that showed the dwarf phenotype of cotton plants by silencing of GhACL5 [18], the role of thermospermine in plant development has rarely been investigated in other plant species so far

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