Diversification and Expression of the PIN, AUX/LAX, and ABCB Families of Putative Auxin Transporters in Populus

Abstract

Intercellular transport of the plant hormone auxin is mediated by three families of membrane-bound protein carriers, with the PIN and ABCB families coding primarily for efflux proteins and the AUX/LAX family coding for influx proteins. In the last decade our understanding of gene and protein function for these transporters in Arabidopsis has expanded rapidly but very little is known about their role in woody plant development. Here we present a comprehensive account of all three families in the model woody species Populus, including chromosome distribution, protein structure, quantitative gene expression, and evolutionary relationships. The PIN and AUX/LAX gene families in Populus comprise 16 and 8 members respectively and show evidence for the retention of paralogs following a relatively recent whole genome duplication. There is also differential expression across tissues within many gene pairs. The ABCB family is previously undescribed in Populus and includes 20 members, showing a much deeper evolutionary history, including both tandem and whole genome duplication as well as probable gene loss. A striking number of these transporters are expressed in developing Populus stems and we suggest that evolutionary and structural relationships with known auxin transporters in Arabidopsis can point toward candidate genes for further study in Populus. This is especially important for the ABCBs, which is a large family and includes members in Arabidopsis that are able to transport other substrates in addition to auxin. Protein modeling, sequence alignment and expression data all point to ABCB1.1 as a likely auxin transport protein in Populus. Given that basipetal auxin flow through the cambial zone shapes the development of woody stems, it is important that we identify the full complement of genes involved in this process. This work should lay the foundation for studies targeting specific proteins for functional characterization and in situ localization.

Down-Regulation of Plasma Intrinsic Protein1 Aquaporin in Poplar Trees Is Detrimental to Recovery from Embolism

“…These genes were found to have, for the same poplar species, the highest amplification efficiency and most stable expression across different tissues (Carraro et al, 2012). Real-time PCR was carried out using three biological replicates per transformed line.…”

Effect of exogenous IAA on tension wood formation by facilitating polar auxin transport and cellulose biosynthesis in hybrid poplar (Populus deltoids × Populus nigra) wood

“…Primers used for amplification are listed in Table S1. The genes selected for transcript analysis are based on previously reported high levels or specific expression in poplar xylem (Suzuki et al 2006;Richet et al 2011;Carraro et al 2012). Transcript relative abundance was calculated as the mean of three biological replicates (three trees per condition) and three analytical replicates.…”

“…The expression of one or more PIN and AUX/LAX genes are up-regulated following exogenous application of IAA and/or gibberellins (Schrader et al 2003). Carraro et al (2012) reported that the expression of PtaPIN1 is strongly up-regulated in the developing internodes of P. tremula × alba by exogenous IAA. In contrast, the mRNA expression of PIN1 gene was significantly decreased in trees after NPA treatment, while a moderate increase in the expression of ABCB1 and AUX2 genes was observed (Figure 3a).…”

“…For example, PIN1 overexpression resulted in the stimulation of auxin efflux in Arabidopsis, and NPA treatment suppressed this effect leading to an [ 3 H]NAA accumulation inside the cells. Additionally, the sensitivity to exogenous IAA and NPA varies from these genes associated with auxin perception, transduction, and transport (Petrášek et al 2006;Carraro et al 2012), which brings about different expression patterns. Probably, the same effect occurs in hybrid poplar stems.…”

“…The intercellular PAT of the Populus is mediated by three families of membranebound protein carriers, including the PIN and ABCB gene families, which contain 16 and 20 members. These are coding primarily for efflux proteins, and the AUX/LAX gene family, which contains eight coding members, for influx proteins (Carraro et al 2012). The expression of these genes may affect signal transmission involved in TW formation and cellulose biosynthesis (Yang and Murphy 2009;Tsuda et al 2010).…”