The Ka/Ks ratios and estimated divergence times for paralogous gene pairs.

<p>The Ka/Ks ratios and estimated divergence times for paralogous gene pairs.</p

Phylogenetic tree of acid invertase proteins from <i>Populus</i>, <i>Arabidopsis</i> and Medicago.

<p>The α clade contains cell-wall invertases (<i>PtrCWINV1</i>-<i>5</i>) and the β clade contains vacuolar invertases (<i>PtrVINV1</i>-<i>3</i>).</p

Expression profiles obtained by RNA-seq for <i>Populus</i> invertase genes in leaf buds.

<p>LLB, latent leaf buds; GLB, leaf buds at germination.</p

Numbers of invertase genes within each plant species according to transcript data.

<p>Numbers of invertase genes within each plant species according to transcript data.</p

Expression analyses obtained by RNA-seq for <i>Populus</i> invertase genes in roots, stems and leaves.

<p>On the x-axis: Rt, roots; St, stems; Lf, leaves.</p

Genome-Wide Identification of the Invertase Gene Family in <i>Populus</i>

<div><p>Invertase plays a crucial role in carbohydrate partitioning and plant development as it catalyses the irreversible hydrolysis of sucrose into glucose and fructose. The invertase family in plants is composed of two sub-families: acid invertases, which are targeted to the cell wall and vacuole; and neutral/alkaline invertases, which function in the cytosol. In this study, 5 cell wall invertase genes (<i>PtCWINV1</i>-<i>5</i>), 3 vacuolar invertase genes (<i>PtVINV1</i>-<i>3</i>) and 16 neutral/alkaline invertase genes (<i>PtNINV1</i>-<i>16</i>) were identified in the <i>Populus</i> genome and found to be distributed on 14 chromosomes. A comprehensive analysis of poplar invertase genes was performed, including structures, chromosome location, phylogeny, evolutionary pattern and expression profiles. Phylogenetic analysis indicated that the two sub-families were both divided into two clades. Segmental duplication is contributed to neutral/alkaline sub-family expansion. Furthermore, the <i>Populus</i> invertase genes displayed differential expression in roots, stems, leaves, leaf buds and in response to salt/cold stress and pathogen infection. In addition, the analysis of enzyme activity and sugar content revealed that invertase genes play key roles in the sucrose metabolism of various tissues and organs in poplar. This work lays the foundation for future functional analysis of the invertase genes in <i>Populus</i> and other woody perennials.</p></div

Multiple alignment of the acid invertase sub-family in <i>Populus</i>.

<p>The boxed region indicates the 13 well-conserved regions from known acid invertases of selected green plants. Arrows indicate the six amino acids that are consistently different between cell-wall and vacuolar invertases.</p

Enzyme activity profiles (acid-soluble, acid-insoluble and neutral invertases) in roots, stems, leaves (A), latent leaf buds and leaf buds at germination (B). Sugar content (sucrose, glucose and fructose) in roots, stems, leaves (C), latent leaf buds and leaf buds at germination (D).

<p>Rt, roots; St, stems; Lf, leaves; LLB, latent leaf buds; GLB, leaf buds at germination.</p

Expression profiles of <i>PtINV</i> gene members in response to salt/cold stress conditions (A-C) and pathogen infection (D).

<p>WT, wild type; WB, with <i>Botryosphaeria</i> infection; Lf, leaves; Rt, Roots.</p

Phylogenetic tree of neutral/alkaline invertase proteins from <i>Populus</i>, <i>Arabidopsis</i> and Medicago.

<p>The α clade (<i>PtrNINV1</i>-<i>6</i>) and the β clade (<i>PtNINV7</i>-<i>12</i>) are indicated. <i>PtNINV13</i>-<i>16</i> are not included. Bootstrap values are generated as a percentage of 1000 repetitions.</p