Laser Microdissection of Specific Stem-Base Tissue Types from Olive Microcuttings for Isolation of High-Quality RNA

Laser Microdissection of Woody and Suberized Plant Tissues for RNA-Seq Analysis

An accurate profile of gene expression at a cellular level can contribute to a better understanding of biological processes and complexities involved in regulatory mechanism of woody plants. Laser microdissection is one technique that allows isolation of specific, target cells or tissue from a heterogeneous cell population. This technique entails microscopic visualization of the selected tissue and use a laser beam to separate the desired cells from surrounding tissue. Initial identification of these cells is made based on morphology and/or histological staining. Some works have been made in several tissues and plant models. However, there are few studies of laser microdissection application in woody species, particularly, lignified and suberized cells. Moreover, the presence of high level of suberin in cell walls can be a big challenge for the application of this approach. In our study it was developed a technique for tissue isolation, using laser microdissection of four different plant cell types (phellogen, lenticels, cortex and xylem) from woody tissues of cork oak (Quercus suber), followed by RNA extraction and RNA-Seq. We tested several methodologies regarding laser microdissection, cryostat equipments, fixation treatments, duration of single-cells collection and number of isolated cells by laser microdissection and RNA extraction procedures. A simple and efficient protocol for tissue isolation by laser microdissection and RNA purification was obtained, with a final method validation of RNA-Seq analysis. The optimized methodology combining RNA-Seq for expression analysis will contribute to elucidate the molecular pathways associated with different development processes of the xylem and phellem in oaks, including the lenticular channels formation.

Stimulation of adventitious root formation by laser wounding in rose cuttings: A matter of energy and pattern

Adventitious root (AR) formation is the basis of vegetative propagation in rose, be it via stem cuttings or via stenting. During this process, wounding plays a pivotal role since cell reprogramming takes place at the tissue adjacent to the wound. We investigated the effects of wounding on AR formation on leafy single-node stem cuttings of the rose rootstock R. canina 'Pfänder' (codes R02-3 and R02-6) and the cut rose cultivar Rosa 'Tan09283' (Registration name 'Beluga'). Laser wounding treatments were based on the assisted removal of tissue layers located in the bark. The positioning of wounding was studied based on two marking directions: along the cutting base (strip pattern) and around the cutting base (ring pattern). Additionally, the effects of external supply of indole-butyric acid (IBA 1 mg L^-1) on rooting were analyzed. Results showed that in order to remove specific tissue layers, the calculation of the laser energy density (J cm^-2) in terms of cutting diameter was necessary. Interestingly, the application of energy densities from 2.5 J cm^-2 up to approximately 8.5 J cm^-2 were sufficient to expose the tissue layers of epidermis up to regions of phloem. Regarding AR formation for R. canina 'Pfänder', characterized by a low rooting response, an increase in the rooting percentage was registered when the laser treatment eliminated the tissue up to phloem proximities. Analysis of the nodal position showed that bud location was a preferential place for AR formation independently of wounding treatment. In case of Rosa 'Tan09283', laser treatments did not reduce its high rooting capacity, but an apparent reduction in rooting quality due to an investment in tissue healing was observed when wounding reached deeper layers such as parenchyma and sclerenchyma. Results also showed a strong AR formation directly from wounded regions in case of Rosa 'Tan09283' specifically when the wound was located below the axillary bud. In conclusion, wounding by assisted-elimination of layers by laser can induce positive effects on AR formation of single-node stem cuttings of the rose if energy applied is able to expose phloem proximities, a longitudinal orientation, and relative position to the axillary bud are considered.