Induced somatic sector analysis of cellulose synthase (CesA) promoter regions in woody stem tissues

The increasing focus on plantation forestry as a renewable source of cellulosic biomass has emphasized the need for tools to study the unique biology of woody genera such as Eucalyptus, Populus and Pinus. The domestication of these woody crops is hampered by long generation times, and breeders are now looking to molecular approaches such as marker-assisted breeding and genetic modification to accelerate tree improvement. Much of what is known about genes involved in the growth and development of plants has come from studies of herbaceous models such as Arabidopsis and rice. However, transferring this information to woody plants often proves difficult, especially for genes expressed in woody stems. Here we report the use of induced somatic sector analysis (ISSA) for characterization of promoter expression patterns directly in the stems of Populus and Eucalyptus trees. As a case study, we used previously characterized primary and secondary cell wall-related cellulose synthase (CesA) promoters cloned from Eucalyptus grandis. We show that ISSA can be used to elucidate the phloem and xylem expression patterns of the CesA genes in Eucalyptus and Populus stems and also show that the staining patterns differ in Eucalyptus and Populus stems. These findings show that ISSA is an efficient approach to investigate promoter function in the developmental context of woody plant tissues and raise questions about the suitability of heterologous promoters for genetic manipulation in plant species.     

CAMBIUM, a process-based model of daily xylem development in Eucalyptus

In hardwoods such as Eucalyptus spp., xylem (wood) is a heterogeneous tissue consisting of multiple cell types. As such, xylem development involves multiple complex interactions. To describe and understand xylem development, and ultimately predict the resultant wood properties, a process-based approach to modelling wood property variation is potentially very useful. In this paper, a new model (CAMBIUM), which incorporates concepts of these processes, is described. CAMBIUM predicts how wood density and fibre and vessel anatomical properties vary from pith-to-bark at a daily time step as a function of changing environmental conditions and a set of simulated physiological processes. Simulations from an existing process-based model of stand development (CABALA) are used as inputs. A key feature of CAMBIUM is a model of the interaction between different xylem cell types. Some weaknesses were identified in the ability of the model to simulate vessel spatial patterns and frequencies, emphasizing the complexities inherent in this aspect of angiosperm wood formation. The model was, however, able to provide realistic estimates of short-term variation and temporal ranges in eucalypt fibre diameter and secondary wall development and wood density.     

Evidence for species-specific clock gene expression patterns in hamster peripheral tissues

Rhythmic oscillations that repeat every 24 h can be found in numerous behavioral and physiological functions. Beside the endogenous master clock in the suprachiasmatic nucleus (SCN), peripheral oscillators exist that can disengage from the master clock rhythm by different mechanisms. The fact that core clock genes in peripheral tissues do not always have the same characteristics as in the SCN suggests that their function may vary in different organs. Additionally, suggestions about species-specific variation in expression peak and nadir times, especially in the testis, led to the need for systematical investigations on clock gene expression patterns in different organs and species under standardized methodological conditions. Therefore, daily gene expression patterns of the clock genes Bmal1, Period1, Period2, Clock, Cryptochrome1 and Cryptochrome2 were recorded at each of eight time points during a 24 hour period in the testis, kidney, liver, spleen and heart of three hamster species (Phodopus sungorus, Phodopus roborovskii and Cricetulus griseus; family: Cricetidae). Clock gene expression was found to be rhythmic in all investigated organs, however with inconsistent results in the testis. Complex cosinor analysis revealed species differences in temporal gene expression patterns regarding their orthophase, number of peaks, and amplitude for all genes and organs with most pronounced differences in the testis. The results of this study strongly indicate that clock gene expression in peripheral tissues is species-specific and that their functions might be at least partly connected to clock-unrelated traits that vary between the investigated species. Further studies should aim at clarifying the specific roles of clock genes in the testis.     

Quercitol plays a key role in stress tolerance of Eucalyptus leptophylla (F. Muell) in naturally occurring saline conditions

Understanding trees adaptation to arid, saline conditions is a major challenge for catchment revegetation in Australia. The accumulation of low molecular weight solutes is an established response of trees to the effects of salt and/or drought stress. Recent studies have shown that quercitol – a cyclitol – contributes significantly towards the adjustment of osmotic potential in some species of Eucalyptus. The present study investigated the role of quercitol in leaf tissues of Eucalyptus leptophylla (F. Muell) under fluctuating environmental stresses. Analysis of leaf tissues from trees growing at distances between 0 and 125 m from hyper-saline lakes suggests that quercitol contributes significantly to the adjustment of osmotic potential induced by drought in E. leptophylla. The presence of substantial concentrations of quercitol in xylem sap suggests that quercitol plays additional roles in signalling amelioration of osmotic stress in myrtaceous species. Quercitol concentrations fluctuate in both xylem and leaf tissues on a seasonal basis, suggesting a form of environmental regulation of solutes. The capacity of soil profiles to store rainwater, rather than proximity to hyper-saline groundwater largely determined osmotic stress in studied trees. Understanding such avoidance/tolerance mechanisms will be crucial to advance tree selection and breeding for stress tolerance.