Genomic Inventory and Transcriptional Analysis of Medicago truncatula Transporters

Abstract

Transporters move hydrophilic substrates across hydrophobic biological membranes and play key roles in plant nutrition, metabolism, and signaling and, consequently, in plant growth, development, and responses to the environment. To initiate and support systematic characterization of transporters in the model legume Medicago truncatula, we identified 3,830 transporters and classified 2,673 of these into 113 families and 146 subfamilies. Analysis of gene expression data for 2,611 of these transporters identified 129 that are expressed in an organ-specific manner, including 50 that are nodule specific and 36 specific to mycorrhizal roots. Further analysis uncovered 196 transporters that are induced at least 5-fold during nodule development and 44 in roots during arbuscular mycorrhizal symbiosis. Among the nodule-and mycorrhiza-induced transporter genes are many candidates for known transport activities in these beneficial symbioses. The data presented here are a unique resource for the selection and functional characterization of legume transporters.

Expression Dynamics of the Medicago truncatula Transcriptome during the Symbiotic Interaction with Sinorhizobium meliloti: Which Role for Nitric Oxide?

“…5) were also down-regulated. This suggests that hormone and redox balance may be modified in the functioning nodule and indicates that dicarboxylic acids replace sugars as the carbon metabolites transported in this organ (White et al, 2007;Benedito et al, 2010). The large number of genes down-regulated is of particular importance, highlighting the high degree of functional specialization of the nodule.…”

Cell type-specific protein and transcription profiles implicate periarbuscular membrane synthesis as an important carbon sink in the mycorrhizal symbiosis

“…5,6 These plant transporter proteins mediate the uptake of the nutrients from the periarbuscular space into the plant cell cytoplasm. 5,7,8 There is currently no evidence for the origin of the precursors for the synthesis of the periarbuscular membrane and the secretion pathway of periarbuscular membrane-specific proteins is unknown.…”

Negotiation, Sanctions, and Context Dependency in the Legume-Rhizobium Mutualism

“…In "Mechanisms for Control of the Mutualism" in the online edition of the American Naturalist, we review the current knowledge of possible mechanisms of control by each party in the legume-rhizobium symbiosis. The plant has a number of possible mechanisms for regulating the allocation of resources to the nodule, including adjusting the oxygen flux into the nodule's cortex (Denison 2000) and regulating the active transport of C 4 dicarboxylic acids (Benedito et al 2010). There is much less known about the mechanisms by which rhizobia can control the outcome, but this situation is due partly to methodological difficulties and partly to a tacit assumption that the plant is in complete control.…”