Gene expression patterns underlying changes in xylem structure and function in response to increased nitrogen availability in hybrid poplar

Abstract

Nitrogen availability has a strong influence on plant growth and development. In this study, we examined the effect of nitrogen availability on xylogenesis in hybrid poplar (Populus trichocarpa ¥ deltoides H11-11). Saplings of hybrid poplar were fertilized for 33 d with either high or adequate levels of ammonium nitrate. We observed enhanced radial growth, wider vessels and fibres and thinner fibre walls in the secondary xylem of high N relative to adequate N plants. These anatomical differences translated into altered hydraulic properties with xylem being more transport efficient but also more vulnerable to drought-induced cavitation in high N plants. The changes in xylem structure and function were associated with differences in gene expression as revealed by the transcriptome analysis of the developing xylem region. We found 388 genes differentially expressed (fold change Ϯ1.5, P-value Յ 0.05), including a number of genes putatively involved in nitrogen and carbohydrate metabolism and various aspects of xylem cell differentiation. Several genes encoding known transcriptional regulators of secondary cell wall deposition were down-regulated in high N plants, corresponding with thinner secondary cell walls in these plants. The results of this study provide us with gene candidates potentially affecting xylem hydraulic and structural traits.

The Hydraulic Architecture of Populus

“…4.2 ). Vessel elements of hybrid poplar saplings had a length of 0.23 mm; mean vessel length was 3-5 cm (Plavcova et al 2011 ;Plavcová et al 2013 ). Fibers had a mean length of 0.58 mm (Plavcova et al 2011 ), similar to what was reported for another hybrid poplar clone (Arend and Fromm 2007 ).…”

“…S1). These anatomical differences were paralleled by higher K S in high N plants compared with plants receiving only adequate N fertilization (adequate N plants) (Hacke et al 2010 ;Plavcová et al 2013 ). Further, high N plants had lower wood densities and were more vulnerable to cavitation than adequate N plants.…”

“…Genes encoding PIPs and TIPs are frequently found to be expressed in the cambial region of poplar species (Schrader et al 2004 ;Goue et al 2008 ;Berta et al 2010 ;Nilsson et al 2010 ;Song et al 2011 ;Plavcová et al 2013 ) and in bulk xylem tissue (Hacke et al 2010 ). RNA in situ hybridization revealed that AQP s were expressed in developing xylem and phloem cells (including living fi bers), and in rays (Almeida-Rodriguez and Hacke 2012 ) (Fig.…”

“…Plants receiving high levels of N (high N plants) exhibited enhanced growth, larger leaves, as well as wider vessels and fi bers (Harvey and van den Driessche 1999 ;Plavcová et al 2013 ). Pitre et al ( 2007 ) reported that high N plants produced fi bers that were wider and shorter compared to the adequate N treatment.…”

Physiological and Genomic Basis of Mechanical-Functional Trade-Off in Plant Vasculature

“…The disturbed hydraulics phenotype is a genetic dissection of the direct relation between aquaporin expression and plant water transport; although there may be components other than Aquaporin that may serve an important role (Sack and Holbrook, 2006;Heinen et al, 2009). It has been shown in hybrid poplar Populus trichocarpa × deltoides, increasing evaporation from leaf surface and perturbed hydraulics is correlated with high aquaporin expression (Plavcová et al, 2013). In common grapevine, Vitis vinifera L. (cv Chardonnay) inhibitors of aquaporin-mediated transport greatly affects both leaf hydraulic conductance and stomatal conductance (Pou et al, 2013).…”