Project description:Despite their different origin and function, both pollen tubes and root hairs share the same sort of apical growth mechanism, i.e., the spatially focused cell expansion at the very apex. Ion fluxes, membrane trafficking, the actin cytoskeleton and their interconnection via signaling networks have been identified as fundamental processes underlying this kind of growth. Several molecules involved in apical growth have been identified, but the genetic basis is far from being fully characterized. We have used Affymetrix Arabidopsis ATH1 GeneChips to obtain the expression profiles of isolated Arabidopsis root hairs. A comparison with the expression profile of flow-sorted pollen grains reveals an overlap in the expression of 4989 genes, which corresponds to 42% of the root hair transcriptome and 76% of the pollen transcriptome, respectively. Our comparison with transcriptional profiles of vegetative tissues by principal component analysis and hierarchical clustering shows a clear separation of these samples comprised of cell types with diffuse growth from the two cell types with apical growth. 277 genes are enriched and 49 selectively expressed, respectively, in root hairs and pollen. From this set of genes emerges an apical growth signature containing novel candidate genes for apical growth determination.
Project description:Despite their different origin and function, both pollen tubes and root hairs share the same sort of apical growth mechanism, i.e., the spatially focused cell expansion at the very apex. Ion fluxes, membrane trafficking, the actin cytoskeleton and their interconnection via signaling networks have been identified as fundamental processes underlying this kind of growth. Several molecules involved in apical growth have been identified, but the genetic basis is far from being fully characterized. We have used Affymetrix Arabidopsis ATH1 GeneChips to obtain the expression profiles of isolated Arabidopsis root hairs. A comparison with the expression profile of flow-sorted pollen grains reveals an overlap in the expression of 4989 genes, which corresponds to 42% of the root hair transcriptome and 76% of the pollen transcriptome, respectively. Our comparison with transcriptional profiles of vegetative tissues by principal component analysis and hierarchical clustering shows a clear separation of these samples comprised of cell types with diffuse growth from the two cell types with apical growth. 277 genes are enriched and 49 selectively expressed, respectively, in root hairs and pollen. From this set of genes emerges an apical growth signature containing novel candidate genes for apical growth determination. Root hairs were isolated from Arabidopsis seedlings and total RNA was isolated for expression profiling on Affymetrix ATH1 arrays. The study was performed with biological duplicates.
Project description:Root hairs are frequently reported to be plastic in response to nutrient supply, but relatively little is known about their development in response to magnesium (Mg) availability, and evidence is scarce about the signals involved in this process. Here, we showed that both density and length of root hairs of Arabidopsis decreased logarithmically with increasing Mg supply in the media , which correlated with the initiation of new trichoblast files and likelihood of trichoblasts to form hairs. Low Mg resulted in greater concentrations of reactive oxygen species (ROS) and Ca2+ in the roots and displayed a stronger tip-focused gradient of ROS and cytosolic Ca2+ concentration ([Ca2+]c) during initiation and elongation of root hairs. This gradient could be eliminated by DPI or BAPTA. Application of either DPI or BAPTA to low Mg treatment blocked the enhanced development of root hairs. The opposite was true when the plants under high Mg were supplied with Ca2+ or PMS. Whole-genome transcriptome data revealed that the maximum differential expressed genes involved in ‘stress’, ‘oxidation reduction’, ‘ion transport and homeostasis’ and ‘cell wall organization’. A greater fraction of morphogenetic H-genes and root hair -specific genes as well as genes involved in ‘cell wall structure’ were up-regulated by 7-d treatment of 0.5 μM Mg but down-regulated by 7-d treatment of 10,000 μM Mg. It is concluded that a distinct and previously poorly characterized response of root hair development to Mg availability is presented in Arabidopsis where ROS and Ca2+ are the signaling molecules that control this response.
Project description:Transcriptional profiling of Arabidopsis thalina seedlings in response to high (140 µM) and low (20 µM) concentrations of chromate (K2CrO4). Low concentrations of chromate (e.g. 40 µM) promoted primary root growth, while high concentrations (e.g. 140 µM) repressed growth and increased formation of root hairs, lateral roots and adventitious roots.
Project description:When grown under phosphate (Pi) deficiency, plants adjust their developmental program and metabolic activity to cope with this nutritional stress. For Arabidopsis, the developmental responses include inhibition of primary root growth and enhanced formation of lateral roots and root hairs. Pi deficiency also inhibits photosynthesis by suppressing the expression of photosynthetic genes. Interestingly, early studies showed that photosynthetic gene expression was also suppressed in roots, a non-photosynthetic tissue. The biological relevance of this phenomenon, however, is not known. In this work, we characterized an Arabidopsis mutant, hps7, which is hypersensitive to Pi deficiency; the hypersensitivity includes an increased inhibition of root growth. HPS7 encodes a tyrosylprotein sulfotransferase (TPST). Accumulation of TPST proteins, but not mRNA, is induced by Pi deficiency. Comparative RNA-Seq analyses indicated that expression of many photosynthetic genes was activated in the roots of hps7. Under Pi deficiency, the expression of the photosynthetic genes in hps7 is further increased, which leads to the enhanced accumulation of chlorophyll, starch, and reactive oxygen species. The increased inhibition of root growth in hps7 under Pi deficiency was completely reversed by growing plants in the dark. Based on these results, we propose that suppression of photosynthetic gene expression in roots is required for sustained root growth under Pi deficiency.
Project description:We report the discovery of a root growth program in Arabidopsis that is independent of a functional quiescent center (QC). In this regulatory program, PHABULOSA (PHB), posttranscriptionally regulated by SHR and SCR, plays a central role. In phb shr and phb scr mutants, root meristem/growth activity recovers significantly. Interestingly, this recovery does not accompany the resurgence of QC cells. PHB regulates apical root growth in stele cells of the root meristem, located proximal to the QC. Our genome-wide investigation suggests that PHB exerts its influence on root growth by regulating auxin-cytokinin homeostasis. Apical root growth was restored when cytokinin levels were genetically reduced in the shr mutant. Conversely, when miRNA-resistant PHB was expressed in the root stele cells, apical root growth and meristem functions were significantly inhibited without blocking the QC identity. Taken together, our investigation reveals two mechanisms through which SHR regulates root growth and stem cell activities: one is to specify and maintain the QC and the other is to regulate the proximal meristem activity through PHB and cytokinin. In this regulation, QC seems to be more involved in maintaining the “growth signal” and thus ensure the indeterminate root growth.
Project description:Zinc (Zn) excess negatively impacts primary root growth in Arabidopsis. The effects of Zn excess on root growth processes in the root tip are not well understood.
Transcriptomics, ionomics and metabolomics were used to examine the specific impact of Zn excess on the root tip (RT) compared to the remaining root (RR).
Zn excess exposure resulted in shortened root apical meristem and elongation zone, with differentiation initiating closer to the tip of root. Zn accumulated at a lower concentration in the RT than in RR.