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Comparative RNA sequencing-based transcriptome profiling of Quercur robur: specific sets of genes involved in taproot and lateral roots emergence
Abstract Root development is well recognized in model plants, with many studies focusing only on primary root growth or lateral root initiation. However, taproot vs lateral root development has rarely been explored using molecular tools, and even less is understood about how the molecular processes engaged in taproot elongation shape the emergence of lateral roots in trees in the time-dependent manner. We address how gene expression is associated with elongation of taproot and lateral root formation of Quercus robur L. In addition, we have analyzed how the exogenous application of hormones and inhibitors shapes the root architecture. We also revealed that lateral root formation and emergence corresponds to expression of genes at specific taproot length points. Therefore, our study suggests that the pattern of gene expression in the taproot tips is involved in the shaping of lateral root growth. In addition, we have shown that lateral roots are characterized by a set of genes that are distinct from those expressed in the taproot tips. Insights from this study contribute to better understanding root development in trees.
Regenerating oak trees with different techniques has long-lasting legacy effects on root development, stem growth and plant physiology
Abstract Regeneration methods can have legacy effects on tree physiology and growth via differential root development and affect forest climate sensitivity. However, there are few studies providing a long-term perspective on how forest regeneration techniques affect root development and physiology of established seedlings that have grown into trees. This study investigates leaf carbon (C), oxygen (O) and nitrogen (N) isotope composition (δ13C, δ18O, δ15N) and stem growth in ⁓20-year-old oak (Quercus robur L.) trees regenerated in two stands by three methods: direct acorn sowing in the field, bare-root planting preceded by root pruning and containerized planting with the root plug intact. Leaf isotopic values were measured three times during summer, together with tree-ring δ13C. Ground penetrating radar analyses indicated that acorn sowing resulted in deep root systems compared shallower root systems of bare-root and containerized trees. Higher annual basal area increment was observed in acorn-sown oaks than in bare-root or containerized oaks. Leaf δ13C, δ18O and δ15N values varied among regeneration origins. Trees with deeper root systems consistently showed lower leaf δ18O values, regardless of the season, which suggests higher uptake of water from deep soil horizons and better leaf hydration. In contrast, oaks with shallower root systems exhibited higher leaf δ18O values, which were positively related with δ13C. More negative leaf δ15N values in shallow-rooted oaks pointed to higher water stress. A lack of correlation between N concentration and intrinsic water-use efficiency (iWUE) for containerized trees suggests that variability in stomatal conductance rates governed iWUE in these shallow-rooted oaks. The lack of correlation between leaf and tree-ring δ13C supports that leaf physiological processes do not necessarily explain latewood isotopic composition. We conclude that regeneration techniques have long-lasting, carry-over effects on root development, plant physiology and tree growth. The findings underscore the importance of considering tree regeneration origin and root distribution when assessing the impact of climate change on tree performance and forest vigor.
Identification of genetics and hormonal factors involved in Quercus robur root growth regulation in different cultivation system
AbstractUnderstanding the molecular processes and hormonal signals that govern root growth is of paramount importance for effective forest management. While Arabidopsis studies have shed light on the role of the primary root in root system development, the structure of root systems in trees is considerably more intricate, posing challenges to comprehend taproot growth in acorn-sown and nursery-cultivated seedlings. In this study, we investigated Quercus robur seedlings using rhizotrons, containers, and transplanted containers to rhizotrons, aiming to unravel the impact of forest nursery practices on processes governing taproot growth and root system development. Root samples were subjected to RNA-seq analysis to identify gene expression patterns and perform differential gene expression and phytohormone analysis. Among studied cultivation systems, differentially expressed genes (DEGs) exhibited significant diversity, where the number of co-occurring DEGs among cultivation systems was significantly smaller than the number of unique DEGs in different cultivation systems. Moreover, the results imply that container cultivation triggers the activation of several genes associated with linolenic acid and peptide synthesis in root growth. Upon transplantation from containers to rhizotrons, rapid enhancement in gene expression occurs, followed by gradual reduction as root growth progresses, ultimately reaching a similar expression pattern as observed in the taproot of rhizotron-cultivated seedlings. Phytohormone analysis revealed that taproot growth patterns under different cultivation systems are regulated by the interplay between auxin and cytokinin concentrations. Moreover, the diversification of hormone levels within the root zone and cultivation systems allows for taproot growth inhibition and prompt recovery in transplanted seedlings. Our study highlights the crucial role of hormone interactions during the early stages of taproot elongation, influencing root system formation across.