Isocitrate lyase plays important roles in plant salt tolerance

Abstract

AbstractBackgroundIsocitrate lyase (ICL) is a key enzyme in the glyoxylate cycle. In a previous study in rice, the expression of the ICL-encoding gene (OsICL) was highly induced by salt stress and its expression was enhanced in transgenic rice lines overexpressingOsCam1–1, a calmodulin (CaM)-encoding gene. CaM has been implicated in salt tolerance mechanisms in plants; however, the cellular mechanisms mediated by CaM are not clearly understood. In this study, the role ofOsICLin plant salt tolerance mechanisms and the possible involvement of CaM were investigated using transgenic plants expressingOsICLorOsCam1–1.ResultsOsICLwas highly expressed in senesced leaf and significantly induced by salt stress in threeOsCam1–1overexpressing transgenic rice lines as well as in wild type (WT). In WT young leaf, althoughOsICLexpression was not affected by salt stress, all three transgenic lines exhibited highly induced expression levels. In Arabidopsis, salt stress had negative effects on germination and seedling growth of theAtICLknockout mutant (Aticlmutant). To examine the roles ofOsICLwe generated the following transgenic Arabidopsis lines: theAticlmutant expressingOsICLdriven by the nativeAtICLpromoter, theAticlmutant overexpressingOsICLdriven by the 35SCaMV promoter, and WT overexpressingOsICLdriven by the 35SCaMV promoter. Under salt stress, the germination rate and seedling fresh and dry weights of theOsICL-expressing lines were higher than those of theAticlmutant, and the two lines with theiclmutant background were similar to the WT. TheFv/Fmand temperature of rosette leaves in theOsICL-expressing lines were less affected by salt stress than they were in theAticlmutant. Finally, glucose and fructose contents of theAticlmutant under salt stress were highest, whereas those ofOsICL-expressing lines were similar to or lower than those of the WT.ConclusionsOsICL, a salt-responsive gene, was characterized in the transgenic Arabidopsis lines, revealing thatOsICLexpression could revert the salt sensitivity phenotypes of theAticlknockout mutant. This work provides novel evidence that supports the role of ICL in plant salt tolerance through the glyoxylate cycle and the possible involvement ofOsCam1–1in regulating its transcription.