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Background: Members of the heat shock protein 90 (Hsp90) class of proteins are evolutionarily conserved molecular chaperones. They are involved in protein folding, assembly, stabilization, activation, and degradation in many normal cellular processes and under stress conditions. Unlike many other well-characterized molecular chaperones, Hsp90s play key roles in signal transduction, cell-cycle control, genomic silencing, and protein trafficking. However, no systematic analysis of genome organization, gene structure, and expression compendium has been performed in the Populus model tree genus to date. Results: We performed a comprehensive analysis of the Populus Hsp90 gene family and identified 10 Populus Hsp90 genes, which were phylogenetically clustered into two major groups. Gene structure and motif composition are relatively conserved in each group. In Populus trichocarpa, we identified three paralogous pairs, among which the PtHsp90-5a/PtHsp90-5b paralogous pair might be created by duplication of a genome segment. Subcellular localization analysis shows that PtHsp90 members are localized in different subcellular compartments. PtHsp90-3 is localized both in the nucleus and in the cytoplasm, PtHsp90-5a and PtHsp90-5b are in chloroplasts, and PtHsp90-7 is in the endoplasmic reticulum (ER). Furthermore, microarray and semi-quantitative real-time RT-PCR analyses show that a number of Populus Hsp90 genes are differentially expressed upon exposure to various stresses. Conclusions: The gene structure and motif composition of PtHsp90s are highly conserved among group members, suggesting that members of the same group may also have conserved functions. Microarray and RT-PCR analyses show that most PtHsp90s were induced by various stresses, including heat stress. Collectively, these observations lay the foundation for future efforts to unravel the biological roles of PtHsp90 genes. [ABSTRACT FROM AUTHOR]

Background: Heat shock proteins (Hsps) are molecular chaperones that are involved in many normal cellular processes and stress responses, and heat shock factors (Hsfs) are the transcriptional activators of Hsps. Hsfs and Hsps are widely coordinated in various biological processes. Although the roles of Hsfs and Hsps in stress responses have been well characterized in Arabidopsis, their roles in perennial woody species undergoing various environmental stresses remain unclear. Results: Here, a comprehensive identification and analysis of Hsf and Hsp families in poplars is presented. In Populus trichocarpa, we identified 42 paralogous pairs, 66.7% resulting from a whole genome duplication. The gene structure and motif composition are relatively conserved in each subfamily. Microarray and quantitative real-time RT-PCR analyses showed that most of the Populus Hsf and Hsp genes are differentially expressed upon exposure to various stresses. A coexpression network between Populus Hsf and Hsp genes was generated based on their expression. Coordinated relationships were validated by transient overexpression and subsequent qPCR analyses. Conclusions: The comprehensive analysis indicates that different sets of PtHsps are downstream of particular PtHsfs and provides a basis for functional studies aimed at revealing the roles of these families in poplar development and stress responses. [ABSTRACT FROM AUTHOR]

The plant hormone auxin is a key regulator of plant development, and its uneven distribution maintained by polar intercellular auxin transport in plant tissues can trigger a wide range of developmental processes. Although the roles of PIN-FORMED (PIN) proteins in intercellular auxin flow have been extensively characterized in Arabidopsis, their roles in woody plants remain unclear. Here, a comprehensive analysis of PIN proteins in Populus is presented. Fifteen PINs are encoded in the genome of Populus, including four PIN1s, one PIN2, two PIN3s, three PIN5s, three PIN6s, and two PIN8s. Similar to Arabidopsis AtPIN proteins, PtPINs share conserved topology and transmembrane domains, and are either plasma membrane- or endoplasmic reticulum-localized. The more diversified expansion of the PIN family in Populus, comparing to that in Arabidopsis, indicates that some auxin-regulated developmental processes, such as secondary growth, may exhibit unique features in trees. More importantly, different sets of PtoPINs have been found to be strongly expressed in the roots, leaves, and cambium in Populus; the dynamic expression patterns of selected PtoPINs were further examined during the regeneration of shoots and roots. This genome-wide analysis of the Populus PIN family provides important cues for their potential roles in tree growth and development. [ABSTRACT FROM AUTHOR]

Background: WUSCHEL (WUS)-related homeobox (WOX) protein family members play important roles in the maintenance and proliferation of the stem cell niche in the shoot apical meristem (SAM), root apical meristem (RAM), and cambium (CAM). Although the roles of some WOXs in meristematic cell regulation have been well studied in annual plants such as Arabidopsis and rice, the expression and function of WOX members in woody plant poplars has not been systematically investigated. Here, we present the identification and comprehensive analysis of the expression and function of WOXs in Populus tomentosa. Results: A genome-wide survey identified 18 WOX encoding sequences in the sequenced genome of Populus trichocarpa (PtrWOXs). Phylogenetic and gene structure analysis revealed that these 18 PtrWOXs fall into modern/WUS, intermediate, and ancient clades, but that the WOX genes in P. trichocarpa may have expanded differently from the WOX genes in Arabidopsis. In the P. trichocarpa genome, no WOX members could be closely classified as AtWOX3, AtWOX6, AtWOX7, AtWOX10, and AtWOX14, but there were two copies of WOX genes that could be classified as PtrWUS, PtrWOX2, PtrWOX4, PtrWOX5, PtrWOX8/9, and PtrWOX11/12, and three copies of WOX genes that could be classified as PtrWOX1 and PtrWOX13. The use of primers specific for each PtrWOX gene allowed the identification and cloning of 18 WOX genes from P. tomentosa (PtoWOXs), a poplar species physiologically close to P. trichocarpa. It was found that PtoWOXs and PtrWOXs shared very high amino acid sequence identity, and that PtoWOXs could be classified identically to PtrWOXs. We revealed that the expression patterns of some PtoWOXs were different to their Arabidopsis counterparts. When PtoWOX5a and PtoWOX11/12a, as well as PtoWUSa and PtoWOX4a were ectopically expressed in transgenic hybrid poplars, the regeneration of adventitious root (AR) was promoted, indicating a functional similarity of these four WOXs in AR regeneration. Conclusions: This is the first attempt towards a systematical analysis of the function of WOXs in P. tomentosa. A diversified expression, yet functional similarity of PtoWOXs in AR regeneration is revealed. Our findings provide useful information for further elucidation of the functions and mechanisms of WOXs in the development of poplars. [ABSTRACT FROM AUTHOR]