Plant-specific histone deacetylases are essential for early as well as late stages of Medicago nodule development

Abstract

Legume and rhizobium can establish a nitrogen-fixing nodule symbiosis. Previous studies have shown that several transcription factors that play a role in (lateral) root development are also involved in nodule development. Chromatin remodelling factors, like transcription factors, are key players in regulating gene expression. However, it has not been studied whether chromatin remodelling genes that are essential for root development get involved in nodule development. Here we studied the role of Medicago histone deacetylases (MtHDTs) in nodule development. Their Arabidopsis orthologs have been shown to play a role in root development. The expression of MtHDTs is induced in nodule primordia and is maintained in nodule meristem and infection zone. Conditional knock-down of their expression in a nodule-specific way by RNAi blocks nodule primordium development. A few nodules still can be formed but their nodule meristems are smaller and rhizobial colonization of the cells derived from the meristem is markedly reduced. Although the HDTs are expressed during nodule and root development, transcriptome analyses indicate that HDTs control the development of these organs in a different manner. During nodule development the MtHDTs positively regulate 3-hydroxy-3-methylglutaryl coenzyme a reductase 1 (MtHMGR1). The decreased expression of MtHMGR1 is sufficient to explain the block of primordium formation.ONE SENTENCE SUMMARYPlant-specific histone deacetylases regulate the expression of 3-hydroxy-3-methylglutaryl-coenzyme A reductases to control root nodule development.

The Regulation of Nodule Number in Legumes Is a Balance of Three Signal Transduction Pathways

“…Recently, chromatin remodeling has been preliminarily shown to be critical to the development of nodule primordia. In a report on bioRxiv, the Bisseling lab suggests M. truncatula histone deacetylases (MtHDTs) are required in nodule primordia, based on conditional RNAi [ 37 ]. However, this requirement appears to be because of the effect of reduced MtHDTs on a single gene: MtHDTs positively regulate 3-hydroxy-3-methylglutaryl coenzyme a reductase 1 ( MtHMGR1 ) in a cell-autonomous manner [ 37 ].…”

“…In a report on bioRxiv, the Bisseling lab suggests M. truncatula histone deacetylases (MtHDTs) are required in nodule primordia, based on conditional RNAi [ 37 ]. However, this requirement appears to be because of the effect of reduced MtHDTs on a single gene: MtHDTs positively regulate 3-hydroxy-3-methylglutaryl coenzyme a reductase 1 ( MtHMGR1 ) in a cell-autonomous manner [ 37 ]. The MtHMGR genes encode enzymes that catalyze the rate-limiting step in a pathway that synthesizes precursors to multiple plant hormones, including cytokinin, brassinosteriods, gibberellin, and abscisic acid [ 38 ] and M. truncatula plants carrying mutations in HMGR1 do not initiate calcium spiking or form nodules [ 39 ].…”