Tortula ruralis (Syntrichia ruralis) is a useful model system for the study of gene control in response to severe water deficit-stress. EST gene discovery efforts utilizing desiccated gametophytes have identified two cDNAs designated Elipa and Elipb with significant similarity to early light-inducible proteins (ELIPs). Elipa is 1006 bp in length, encoding a 212 amino acid deduced polypeptide (ELIPa) with a predicted molecular mass of 23.3 kDa and pI of 5.57. Elipb is 997 bp in length, encoding a 224 amino acid deduced polypeptide (ELIPb) with a predicted molecular mass of 24.4 kDa and pI of 9.27. Phylogenetic analysis demonstrated that ELIPa and ELIPb are reproducibly grouped with ELIP sequences derived from desiccation-tolerance tissues. RNA blot hybridization was used to analyse Elipa and Elipb mRNA abundance in response to a variety of stresses. Elipa steady-state transcript levels increased in response to slow desiccation, rapid desiccation/rehydration, salinity, ABA, and rehydration in high light. The Elipb transcript was only detectable in response to ABA or rehydration in high light. It is postulated that ELIPa and ELIPb are an adaptive response to stress-induced photodamage within the moss chloroplast, and play a key role in the protection and/or repair of the photosynthetic apparatus.

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(S.M.G., X.L., Xinlu C., R.A.B., M.A.J.)Insertional mutagenesis of Arabidopsis (Arabidopsis thaliana) was used to identify a novel recessive mutant, designated resurrection1 (rst1), which possesses a dramatic alteration in its cuticular waxes and produces shrunken nonviable seeds due to arrested embryo development. The RST1 gene sequence associated with these phenotypes was verified by three independent, allelic, insertion mutants, designated rst1-1, rst1-2, and rst1-3, with inserts in the first exon, 12th intron, and fourth exon, respectively. These three rst1 allelic mutants have nearly identical alterations in their wax profiles and embryo development. Compared to wild type, the wax on rst1 inflorescence stems is reduced nearly 60% in total amount, has a proportional reduction in aldehydes and aldehyde metabolites, and has a proportional increase in acids, primary alcohols, and esters. Compared to wild type, the C 29 alkanes on rst1 are nearly 6-fold lower, and the C 30 primary alcohols are 4-fold higher. These results indicate that rst1 causes shunting of most wax precursors away from alkane synthesis and into the primary-alcoholproducing branch of the pathway. In contrast to stems, the wax on rst1 mutant leaves increased roughly 43% in amount relative to the wild type, with the major increase occurring in the C 31 and C 33 alkanes. Unique among known wax mutants, approximately 70% of rst1 seeds are shrunken and nonviable, with these being randomly distributed within both inflorescence and silique. Viable seeds of rst1 are slightly larger than those of wild type, and although the viable rst1 seeds contain more total triacylglycerol-derived fatty acids, the proportions of these fatty acids are not significantly different from wild type. Shrunken seeds contain 34% of the fatty acids of wild-type seeds, with proportionally more palmitic, stearic, and oleic acids, and less of the longer and more desaturated homologs. Histological analysis of aborted rst1 seeds revealed that embryo development terminates at the approximate heart-shaped stage, whereas viable rst1 and wild-type embryos develop similarly. The RST1 gene encodes a predicted 1,841-amino acid novel protein with a molecular mass of 203.6 kD and a theoretical pI of 6.21. The RST1 transcript was found in all tissues examined including leaves, flowers, roots, stems, and siliques, but accumulation levels were not correlated with the degree to which different organs appeared affected by the mutation. The new RST1 gene reveals a novel genetic connection between lipid synthesis and embryo development; however, RST1's exact role is still quite unknown. The degree to which RST1 is associated with lipid signaling in development is an important focus of ongoing studies.Plant lipids, including phospholipids (Meijer and Munnik, 2003), sterols (He et al., 2003), sphingolipids (Sperling and Heinz, 2003), fatty acids, and their derivatives like jasmonate (Turner et al., 2002;Weber, 2002), can serve as important signal molecules in the regulation of plant development. Re...

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Expression profiles of 12 class A rice heat shock transcription factor genes (OsHsfAs) were analyzed by semi-quantitative reverse transcriptase polymerase chain reaction. The OsHsfA genes exhibited tissue-specific expressions under normal condition. OsHsfA1a, A2d, and A9 were predominantly expressed in young spike. Expression responses of the 12 OsHsfAs under abiotic stresses were analyzed in the shoots of rice seedling. Most OsHsfA genes responded quickly to heat stress except for OsHsfA1a, A3, and A9 which were almost unaffected. In particular, OsHsfA2a expression in response to heat stress was highest among the heat shock factors examined. However, the majority of the increased OsHsfAs expression responses to salt, polyethylene glycol (PEG), and cold treatments primarily occurred during the later stages (3 to 24 h) of stress exposure. Furthermore, most of OsHsfA gene expressions were little affected and only a few (OsHsfA3, A4d, A7, and A9) genes had slow responses to cold treatment. The results indicate that the transcript levels of OsHsfAs during heat stress exposure were distinct from those of plants subjected to salt, PEG, and cold stresses, suggesting that there might be different regulatory networks between heat and non-heat stress.

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OsHSP50.2, an HSP90 family gene up-regulated by heat and osmotic stress treatments, positively regulates drought stress tolerance probably by modulating ROS homeostasis and osmotic adjustment in rice. Heat-shock proteins (HSPs) serve as molecular chaperones for a variety of client proteins in abiotic stress response and play pivotal roles in protecting plants against stress, but the molecular mechanism remains largely unknown. Here, we report an HSP90 family gene, OsHSP50.2, which acts as a positive regulator in drought stress tolerance in rice (Oryza sativa). OsHSP50.2 was ubiquitously expressed and its transcript level was up-regulated by heat and osmotic stress treatments. Overexpression of OsHSP50.2 in rice reduced water loss and enhanced the transgenic plant tolerance to drought and osmotic stresses. The OsHSP50.2-overexpressing plants exhibited significantly lower levels of electrolyte leakage and malondialdehyde (MDA) and less decrease of chlorophyll than wild-type plants under drought stress. Moreover, the OsHSP50.2-overexpressing plants had significantly higher SOD activity under drought stress compared with the wild type. These results imply that OsHSP50.2 positively regulates drought stress tolerance in rice, probably through the modulation of reactive oxygen species (ROS) homeostasis. Additionally, the OsHSP50.2-overexpressing plants accumulated significantly higher content of proline than the wild type under drought stress, which contributes to the improved protection ability from drought stress damage via osmotic adjustment. Our findings reveal that OsHSP50.2 plays a crucial role in drought stress response, and it may possess high potential usefulness in drought tolerance improvement of rice.