Identification of genes regulated by ammonium availability in the roots of maritime pine trees

Abstract

Conifers have a preference for ammonium over nitrate as the main inorganic nitrogen source. However, it is unknown how changes in nitrogen nutrition may affect transcription profiles. In this study, microarray analysis and suppressive subtraction hybridization were used to identify differentially expressed genes in the roots of maritime pine exposed to changes in ammonium availability. A total of 225 unigenes that were differentially regulated by changes in ammonium nutrition were identified. Most of the unigenes were classified into seven functional categories by comparison with sequences deposited in the databases. A significant proportion of these genes were encoded for ammonium-regulated proteins of unknown functions. The differential expression of selected candidate genes was further validated in plants subjected to ammonium excess/deficiency. The transcript levels of representative genes were compared in maritime pine roots, 1, 15 and 35 days after nutritional treatments. Gene expression patterns suggest the existence of potential links between ammonium-responsive genes and genes involved in amino acid metabolism, particularly in asparagine biosynthesis and utilization. Functional analyses and exploration of the natural variability in maritime pine populations for a number of relevant genes are underway.

Nitrogen Economy and Nitrogen Environmental Interactions in Conifers

“…More recently the role of AMP1 in maritime pine has been linked to N acquisition. Excess ammonium induces the expression of AMP1 [24], and functional analyses performed with purified protein supports the function of AMP1 in the regulation of ammonium ion flux into pine roots [106]. These results highlight the connections between pathogen attack and N metabolism, a topic that warrants further research efforts.…”

“…It has been found that the ammonium regulated AMP1 protein [24,106] is also upregulated at the early stages of ectomycorriza formation and therefore might be involved in the regulation of N transfer from ectomycorrizal fungi to plant hosts [115]. Following transfer at the mycorrhizal interface, N is incorporated into the amides glutamine and asparagine [115].…”

“…N availability affects wood properties by modifying wood density, altering cell wall thickness and influencing fiber length [22]. At the molecular level, a number of studies have shown that specific genes are differentially regulated in stems [23] and roots [24].…”

Gene expression profiling in the stem of young maritime pine trees: detection of ammonium stress-responsive genes in the apex

“…The highest levels of AMP transcripts were present in the apex, with lower abundances in other sections, except for a peaking bulk in section 4, which represented about 30% of the maximal observed expression. AMP1 is a member of the plant AMP b-barrelin family and could have a role in the regulation of ammonium nutrition in maritime pine roots (Canales et al 2010(Canales et al , 2011. In contrast, the LPT and MT genes were almost exclusively expressed in the upper part of the stem, suggesting that they are mainly associated with the function of meristematic cells.…”

“…In a recent paper, we investigated the effects of ammonium availability on the transcriptome of maritime pine roots using a combination of microarray analysis and suppressive subtraction hybridization (Canales et al 2010).…”