Browsing by Author "Lyall, Rafe"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    Open Access
    Comparative analysis of desiccation responses in three Xerophyta species at two stages of seedling development
    (2025) Ngcala, Mamosa; Illing, Nicola; Ingle Robert; Nikoloski, Zoran; Lyall, Rafe
    Vegetative desiccation tolerance (VDT) is a rare trait among flowering plants, enabling the adult tissues of certain species, known collectively as resurrection plants, to survive near-total water loss and revive upon rehydration. This study used a seedling model to investigate VDT at two developmental stages, pre-leaf and two-leaf stage, across three Xerophyta species: the poikilochlorophyllous Xerophyta schlechteri, and X. humilis, and the homoiochlorophyllous X. elegans. By analyzing changes in cellular ultrastructure, gene expression, and metabolite and lipid concentrations, the aim was to identify core conserved VDT mechanisms in these three Xerophyta species, as well as differences between poikilochlorophyllous and homoiochlorophyllous species in the same genus. Transcriptomic analysis showed that the key seed master maturation transcription factors (TFs) ABI3A and ABI5A, were up-regulated in dry pre-leaf seedlings but no expression was detected in two-leaf seedlings. In contrast, the ABRE binding factor, ABFA, was highly expressed in dry tissues at all developmental stages across all species, suggesting a potential role in VDT. A three-way comparison was used to identify gene orthogroups (OGs) that showed the same response to desiccation across all three Xerophyta species: these 370 up-regulated and 335 down-regulated OGs potentially represented a core set of desiccation-responsive genes in Xerophyta species. Promoter regions of these core OGs were enriched with binding sites for Xerophyta specific expanded TF families, including Heat Shock Factors (HSFs), A-T hook factors (AHLs), and C2H2 Zinc Finger Proteins (ZATs). The gene ontology enrichment showed that the HSF, AHL, and ZAT motif containing OGs that were up-regulated are involved in water deprivation, abscisic acid response, and oxidative stress response processes, whereas the down-regulated OGs are involved in growth and development related processes. Notably, some of the up-regulated HSF motif-containing target OGs included WRKY TFs, stachyose synthase, and solanesyl diphosphate synthase 2, which are involved in stress-related functions enhancing VDT. Metabolite analysis demonstrated that the osmoprotectants proline, sucrose, and trehalose accumulated in dry tissues at both developmental stages of all three Xerophyta species. Moreover, differences in cellular ultrastructure including chloroplast organization were investigated by transmission electron microscopy, comparing a detailed dehydration rehydration time course of poikilochlorophyllous X. schlechteri to homoiochlorophyllous X. elegans. This analysis revealed that desiccation-induced ultrastructural changes, such as vacuolation, chloroplast centralization, and starch degradation, typically observed in adult tissues, were also prevalent in the two-leaf seedlings of X. elegans and X. schlechteri. Notably, complete disassembly of the thylakoid membranes was observed in X. schlechteri but not in X. elegans. These results align with the significant reduction of monogalactosyldiacylglycerol, a major galactolipid involved in chloroplast function. The results of this study highlight differences between the poikilochlorophylly and homoiochlorophylly strategies, as well as conserved molecular responses to desiccation in Xerophyta species, providing insights into the evolution of VDT
  • Thumbnail Image
    Item
    Open Access
    Regulation of desiccation tolerance in Xerophyta seedlings and leaves
    (2016) Lyall, Rafe; Illing, Nicola; Ingle, Robert A
    A small, diverse group of angiosperms known as resurrection plants display vegetative desiccation tolerance and can survive loss of up to 95% of cellular water, a feat only seen in the seeds and pollen of other angiosperms. Xerophyta humilis is a resurrection plant native to Southern Africa that has been the target of previous transcriptomic and proteomic studies into the mechanisms of plant desiccation tolerance. The aim of this study was to investigate the hypothesis that vegetative desiccation tolerance is derived from the networks that control desiccation tolerance in seeds and germinating seedlings in angiosperms, particularly the epigenetically silenced seed maturation genes. Germinating seedlings of X. humilis and the related resurrection plant X. viscosa were found to be VDT from the earliest stages of germination, and exhibited the characteristic vegetative trait of poikilochlorophylly as seen in mature leaves. The X. humilis desiccation transcriptome comprising 76,768 distinct gene clusters was successfully assembled from sequencing samples at five relative water contents (100%, 80%, 60%, 40% and 5%) to identify the networks activated in response to water loss. Desiccation was associated with successive waves of transcription factor induction, as well as widespread down-regulation of histone modification enzymes. Many seed-specific genes, such as late embryogenesis abundant (LEA) proteins, seed storage proteins and oleosins, were induced in vegetative tissue. LEA transcripts in particular were highly up-regulated during desiccation, and the large number of distinct LEA transcripts (over 150) suggests possible LEA gene expansion in Xerophyta compared to desiccation-sensitive plants. Components of the PYL/SnRK2/ABF ABA-signalling pathway were also induced, although the ABF transcription factors activated in response to desiccation were most similar to those induced by drought in A. thaliana rather than seed maturation. Of the canonical seed master regulators (such as the LEC1/ABI3/FUS3/LEC2 network and ABI5) only three ABI3 transcripts were expressed, all of which encoded proteins lacking the seed motif-binding B3-domain. The results of this study suggest that vegetative desiccation tolerance in X. humilis is not associated with re-activation of seed master regulators in vegetative tissue, but may instead involve activation of seed genes by vegetative drought response regulators.
  • Thumbnail Image
    Item
    Open Access
    The window of desiccation tolerance shown by early-stage germinating seedlings remains open in the resurrection plant, Xerophyta viscosa
    (Public Library of Science, 2014) Lyall, Rafe; Ingle, Robert A; Illing, Nicola
    Resurrection plants are renowned for their vegetative desiccation tolerance (DT). While DT in vegetative tissues is rare in angiosperms, it is ubiquitous in mature orthodox seeds. During germination, seedlings gradually lose DT until they pass a point of no return, after which they can no longer survive dehydration. Here we investigate whether seedlings of the resurrection plant Xerophyta viscosa ever lose the capacity to establish DT. Seedlings from different stages of germination were dehydrated for 48 hours and assessed for their ability to recover upon rehydration. While a transient decline in the ability of X. viscosa seedlings to survive dehydration was observed, at no point during germination was the ability to re-establish DT completely lost in all seedlings. Pre-treatment of seedlings with PEG or sucrose reduced this transient decline, and improved the survival rate at all stages of germination. Additionally, we observed that the trait of poikilochlorophylly (or loss of chlorophyll) observed in adult X. viscosa leaves can be induced throughout seedling development. These results suggest that the window of DT seen in germinating orthodox seeds remains open in X. viscosa seedlings and that vegetative DT in Xerophyta species may have evolved from the ability to retain this program through to adulthood.