Protection mechanisms in the resurrection plant Xerophyta viscosa: Cloning, expression, characterisation and role of XvINO1, a gene coding for a myo-inositol 1-phosphate synthase

Department of Molecular and Cellular Biology, A University of Cape Town, 7701, Rondebosch, Cape Town, South Africa
Functional Plant Biology (Impact Factor: 3.15). 01/2008; 35(1):26--39. DOI: 10.1071/FP07142


We have used reverse transcription-PCR coupled with 5 -and 3 -RACE to isolate a full length INO1 cDNA (1692 bp with an ORF of 1530) from the resurrection plant Xerophyta viscosa Baker. XvINO1 encodes 510 amino acids, with a predicted MW of 56.7kD and contains four sequence motifs that are highly conserved in plant myo-inositol-1-phosphate synthases (MIPS, EC5.5.1.4), the enzyme that catalyses the first step in the formation of myo-inositol (Ino). Northern and western analyses show that the transcript and protein are constitutively present in leaves but their expression increases, temporarily, in response to both accumulative salt stress (∼300 mM NaCl) and desiccation (to 5% relative water content). Leaf Ino concentration increases 40-fold during the first 6 h of salt stress, and levels of this and other carbohydrates (galactinol, sucrose, raffinose, stachyose and hexoses) remain elevated relative to control leaves for the duration of salt stress treatment. The timing and pattern of accumulation of these carbohydrates differ under desiccation stress and we propose that they perform different functions in the respective stresses. These are elaborated in discussion of our data.

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    • "Recent advances in sequencing technologies and assembly algorithms have facilitated the reconstruction of the entire transcriptome by deep RNA sequencing (RNA-seq), even without a reference genome, therefore, this is also applicable to resurrection plants (Table 1). Gene expression studies and EST sequencing have been performed in some resurrection species, such as the moss T. ruralis (Scott and Oliver, 1994; Wood and Oliver, 1999; Zeng et al., 2002; Oliver et al., 2004), the clubmosses Selaginella lepidophylla and Selaginella tamariscina (Zentella et al., 1999; Iturriaga et al., 2006; Liu et al., 2008), the monocot species Sporobolus stapfianus (Neale et al., 2000; Le et al., 2007), X. viscosa (Mundree et al., 2000; Mowla et al., 2002; Lehner et al., 2008), X. humilis (Collett et al., 2003, 2004; Illing et al., 2005; Mulako et al., 2008), and X. villosa (Collett et al., 2004), and the dicot species C. plantagineum (Bockel et al., 1998). In these studies, the cDNA libraries for EST sequencing were either generated from one or two physiological conditions (dehydrated and rehydrated gametophytes/fronds/roots or leaves) and restricted in number thereby not always reflecting global transcript changes. "
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    ABSTRACT: Most higher plants are unable to survive desiccation to an air-dried state. An exception is a small group of vascular angiosperm plants, termed resurrection plants. They have evolved unique mechanisms of desiccation tolerance and thus can tolerate severe water loss, and mostly adjust their water content with the relative humidity in the environment. Desiccation tolerance is a complex phenomenon and depends on the regulated expression of numerous genes during dehydration and subsequent rehydration. Most of the resurrection plants have a large genome and are difficult to transform which makes them unsuitable for genetic approaches. However, technical advances have made it possible to analyze changes in gene expression on a large-scale. These approaches together with comparative studies with non-desiccation tolerant plants provide novel insights into the molecular processes required for desiccation tolerance and will shed light on identification of orphan genes with unknown functions. Here, we review large-scale recent transcriptomic, proteomic, and metabolomic studies that have been performed in desiccation tolerant plants and discuss how these studies contribute to understanding the molecular basis of desiccation tolerance.
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    • "While the presence of LEA and LEA-like protein gene sequences among the dehydration-induced EST dataset is in line with a presumed role for these polypeptides in the response to water stress, several other genes associated with stress responses were also found. For example, genes encoding: myo-inositol-1-phosphate synthase which controls synthesis of an osmolyte, myo-inositol, implicated in desiccation tolerance [37,38]; AHA-1, a stress-regulated activator of the ATPase activity of molecular chaperone Hsp90 [39]; and glutathione peroxidase, which catalyses the reduction of hydroxyperoxides by glutathione and is important in the response to oxidative stress (reviewed in [40]). "
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