Novel conserved segments are associated with differential expression patterns for Pinaceae dehydrins

Dehydrins are thought to play an essential role in the response, acclimation and tolerance to different abiotic stresses, such as cold and drought. These proteins have been classified into five groups according to the presence of conserved and repeated motifs in their amino acid sequence. Due to their putative functions in the response to stress, dehydrins have been often used as candidate genes in studies on population variability and local adaptation to environmental conditions. However, little is still known regarding the differential role played by such groups or the mechanism underlying their function. Based on the sequences corresponding to dehydrins available in public databases we have isolated eight different dehydrins from cDNA of Pinus pinaster. We have obtained also their genomic sequences and identified their intron/exon structure. Quantitative RT-PCR analysis of their expression pattern in needles, stems and roots during a severe and prolonged drought stress, similar to the ones trees must face in nature, is also reported. Additionally, we have identified two amino acid motifs highly conserved and repeated in Pinaceae dehydrins and absent in angiosperms, presumably related to the divergent expression profiles observed.     

Wood density of silver fir reflects drought and cold stress across climatic and biogeographic gradients

Climate influences wood density and this relationship affects the ability of conifer forests to uptake and store carbon. Some conifer species can show mixed responses to long-term climate variability in their within-ring width and density patterns. Here we analyze if tree-ring width and density differently respond to seasonal climate variability in silver fir (Abies alba) forests from the Spanish Pyrenees subjected to cold and Mediterranean influences. In these forests, early growing-season dry conditions increase minimum wood density, possibly by reducing lumen diameter and lowering growth rates. Cold conditions during the late growing season are associated to a decrease in maximum wood density, probably through a reduction in the lignification and thickening rates of latewood tracheids. We test if these associations follow climatic and biogeographic patterns since the Mediterranean influence, characterized by late-summer storms which alleviate drought stress, is prevalent eastwards in this region. Silver-fir intra-annual width and wood density data showed mixed responses to climate. Minimum wood density negatively responded to spring precipitation, particularly in dry sites forming the southernmost distribution limit of the species. Maximum wood density positively responded to mean maximum temperatures and sunshine duration during late summer and early autumn, mainly in eastern sites subjected to a dominant Mediterranean influence where late-summer drought stress is expected to be low. More extreme climate conditions including dry spells could shift minimum wood density and reduce hydraulic conductivity and growth in conifer species as silver fir which dominate mesic sites. Warmer conditions would lead to denser latewood in silver fir if accompanied by longer durations of sunshine.     

Variable Chlorophyll a Fluorescence and CO(2) Uptake in Water-Stressed White Spruce Seedlings

Regulation of photosynthetic activity can contribute to the prevention of photodamage in stress resistant plants during exposure to drought or low temperatures. Responses to increasing levels of water stress were examined in seedlings of the stress resistant forest conifer, white spruce (Picea glauca [Moench.] Voss). Some seedlings were grown under aseptic in vitro conditions and others in pots. In relatively resistant in vivo seedlings, photosynthetic activities changed slowly in response to increasing water stress. Highly sensitive in vitro seedlings responded to water deficits similarly to in vivo seedlings but over a much shorter time scale. Fluorescence, CO₂ exchange, and stomatal conductance data reported here suggest possible mechanisms for the regulation of photochemical activity in these plants.     

毛尖紫萼藓干旱胁迫cDNA文库的构建

干旱胁迫是影响植物生长发育的主要环境因素,严重影响农作物的产量。解决这个问题的有效途径是培育和利用优良的抗旱品种。应用比较功能基因组学方法筛选抗旱相关基因,并通过基因工程培育抗旱品种已成为植物遗传资源与品种改良研究的重要内容。毛尖紫萼藓（Grimmia pilifera）是典型旱生藓类,生长在向阳的裸岩上,具有很强的抗旱能力,是很好的抗旱基因资源。本研究采用SMART技术构建毛尖紫萼藓干旱cDNA文库,文库滴度为2.8×10⁵ pfu·mL^-1,重组率为91.7%,插入片段大小为500~2 000 bp,平均为800 bp。通过测序我们获得了1 045条ESTs,其中高质量的996条,通过拼接获得875个Unigenes,为进一步筛选抗旱相关基因奠定了基础。     

Transcriptional analysis of differentially expressed genes in response to stem inclination in young seedlings of pine

The gravitropic response in trees is a widely studied phenomenon, however understanding of the molecular mechanism involved remains unclear. The purpose of this work was to identify differentially expressed genes in response to inclination using a comparative approach for two conifer species. Young seedlings were subjected to inclination and samples were collected at four different times points. First, suppression subtractive hybridisation (SSH) was used to identify differentially regulated genes in radiata pine (Pinus radiata D. Don). cDNA libraries were constructed from the upper and lower part of inclined stems in a time course experiment, ranging from 2.5 h to 1 month. From a total of 3092 sequences obtained, 2203 elements were assembled, displaying homology to a public database. A total of 942 unigene elements were identified using bioinformatic tools after redundancy analysis. Of these, 614 corresponded to known function genes and 328 to unknown function genes, including hypothetical proteins. Comparative analysis between radiata pine and maritime pine (Pinus pinaster Ait.) was performed to validate the differential expression of relevant candidate genes using qPCR. Selected genes were involved in several functional categories: hormone regulation, phenylpropanoid pathway and signal transduction. This comparative approach for the two conifer species helped determine the molecular gene pattern generated by inclination, providing a set of Pinus gene signatures that may be involved in the gravitropic stress response. These genes may also represent relevant candidate genes involved in the gravitropic response and potentially in wood formation.     

Functional dissection of drought-responsive gene expression patterns in Cynodon dactylon L.

Water deficit is one of the main abiotic factors that affect plant productivity in subtropical regions. To identify genes induced during the water stress response in Bermudagrass (Cynodon dactylon), cDNA macroarrays were used. The macroarray analysis identified 189 drought-responsive candidate genes from C. dactylon, of which 120 were up-regulated and 69 were down-regulated. The candidate genes were classified into seven groups by cluster analysis of expression levels across two intensities and three durations of imposed stress. Annotation using BLASTX suggested that up-regulated genes may be involved in proline biosynthesis, signal transduction pathways, protein repair systems, and removal of toxins, while down-regulated genes were mostly related to basic plant metabolism such as photosynthesis and glycolysis. The functional classification of gene ontology (GO) was consistent with the BLASTX results, also suggesting some crosstalk between abiotic and biotic stress. Comparative analysis of cis-regulatory elements from the candidate genes implicated specific elements in drought response in Bermudagrass. Although only a subset of genes was studied, Bermudagrass shared many drought-responsive genes and cis-regulatory elements with other botanical models, supporting a strategy of cross-taxon application of drought-responsive genes, regulatory cues, and physiological-genetic information.     

Identification of a drought-induced rice gene, OsSAP, that suppresses Bax-induced cell death in yeast

We identified rice genes that might be involved in drought stress tolerance by virtue of their anti-apoptotic activity. Potential anti-apoptosis related genes were identified by screening an Oryza sativa cDNA library derived from drought stressed tissues in a yeast functional assay. About 28 O. sativa cDNAs promoted yeast survival following engagement of Bax-induced apoptosis. An O. sativa cDNA encoding R12H780 was a highly conserved putative senescence-associated-protein (OsSAP). OsSAP was both highly and rapidly expressed in response to drought stress. Additionally, OsSAP was found to be localized to the mitochondria. Overall, OsSAP represents a new type of Bax suppressor related gene and endows multiple stress tolerance in yeast.     

Differential quantitative regulation of specific gene groups and pathways under drought stress in rice

Abiotic stresses like drought are detrimental for growth and development and lead to loss in crop production. To be able to adapt and survive under such adverse conditions, synchronous regulation of a rather large number of genes is required. Here, we have used a bioinformatics approach to identify gene groups and associated pathways from microarray and RNA-seq experiments that are restricted in their gene expression amplitude within fold change intervals (FCI) under drought stress conditions. We find that the expression of genes as functional groups is coordinated quantitatively, in a fold change specific manner, and differs among three rice cultivars distinct in their drought stress response. By networking these groups and further categorization into components like ubiquitin proteasome system, we identify relatively less studied E2 ubiquitin conjugating enzyme coding genes as an important constituent of differential drought stress response in rice. By extending this approach to find hexamer DNA motifs in the upstream promoter regions of genes within the FCIs under stress, we find that genes with strong to very strong or a moderate expression under stress are coordinated through cis-regulatory motifs. Few of these, such as TSO1, L-Box, PE1, GT binding site, ABRE/G-box or AP2/ERF binding site can be candidate cis-regulatory motifs to coordinate fold change limited gene expression under drought stress. This work thus provides an insight into a quantitative regulation of gene expression under drought stress in rice and a useful resource for designing approaches towards coordinating the expression of identified candidate genes under stress in order to achieve drought tolerance in rice.     

Interactive effects of ozone and drought stress on pigments and activities of antioxidative enzymes in Pinus halepensis

The aim of this study was to investigate the interactive effects of ozone (O₃) and drought on pigments and antioxidant enzymes of Aleppo pine (Pinus halepensis). Two‐year‐old seedlings were exposed in open‐top chambers to charcoal‐filtered air or non‐filtered air plus an additional 40 nL L^?1 of ozone. After 20 months of O₃ exposure, a subset of plants was subjected to drought stress by withholding water supply for 11 d. Ozone induced higher guaiacol peroxidase, catalase and KCN‐resistant superoxide dismutase (SOD) activities in young needles, while drought stress increased glutathione reductase and CuZnSOD. One‐year‐old needles showed lower capacity to activate these enzymes in response to stress. Both ozone and drought activated the xanthophyll cycle pool and reduced chlorophyll contents in both current and 1‐year‐old needles. The combined effects of ozone and drought decreased antioxidant enzyme activities and the capacity of recovering after re‐watering. Similarly, interactive effects of O₃ and drought reduced xanthophyll‐mediated photoprotection capacity in 1‐year‐old needles but induced a higher conversion of the cycle in current‐year needles. These results showed that ozone modified the Aleppo pine response to drought stress, suggesting that this pollutant might be reducing the ability of this species to withstand other environmental stresses.     

Plasticity of morphological and physiological traits in response to different levels of irradiance in seedlings of silver fir (Abies alba Mill)

The ability of silver fir ( Abies alba Mill.) to acclimate to different levels of irradiance was tested with 3-year-old seedlings, grown for 2 years in a nursery close to Nancy (eastern France) under 100, 48, 18 and 8% of incident irradiance (neutral shade nets). Growth, total nutrients in needles, maximal carboxylation rate ( V _cmax), maximal light driven electron flow ( J _max) and the relative amount of nitrogen allocated to photosynthetic processes (carboxylation, bioenergetics, light harvesting) were investigated. The sensitivity to drought stress was assessed among the phenotypes resulting from light acclimation. Leader-shoot and branch elongation were greatest under 18% irradiance. Total seedling biomass, root-to-total biomass ratio, total leaf area, leaf mass-to-area ratio and needle-area based nitrogen content responded positively to increasing irradiance while leaf area ratio decreased. Both V _cmax and J _max increased by a factor of 1.6 and 1.8, respectively, from the lowest to the highest irradiance but the ratio J _max/ V _cmax remained stable. All these parameters, expressed on a projected needle area basis, remained within the lower range of values measured for broadleaved trees. Relative allocation of needle N to the different components of the photosynthetic apparatus was very low: 12, 3 and 7% of total nitrogen were invested in carboxylation, bioenergetics and light harvesting, respectively. The relative allocation of nitrogen to carboxylation and bioenergetics remained stable while that to light harvesting decreased with increasing irradiance. During drought, seedlings pre-acclimated to shade closed their stomata at higher predawn needle water potential than those which were grown under higher irradiance. Critical temperature for PSII photochemistry in needles was unaffected by irradiance and was close to 47°C. Drought significantly increased the critical temperature up to 51°C. In general, the amplitude of responses of silver fir to changing irradiance (phenotypic plasticity) was smaller than that recorded in broadleaved species.     

Identification and expression analysis of group 3 LEA family genes in sorghum [Sorghum bicolor (L.) Moench]

Sorghum with its remarkable adaptability to drought and high temperature provides a model system for grass genomics and resource for gene discovery especially for abiotic stress tolerance. Group 3 LEA genes from barley and rice have been shown to play crucial role in abiotic stress tolerance. Here, we present a genome-wide analysis of LEA3 genes in sorghum. We identified four genes encoding LEA3 proteins in the sorghum genome and further classified them into LEA3A and LEA3B subgroups based on the conservation of LEA3 specific motifs. Further, expression pattern of these genes were analyzed in seeds during development and vegetative tissues under abiotic stresses. SbLEA3A group genes showed expression at early stage of seed development and increased significantly at maturity, while SbLEA3B group genes expressed only in matured seeds. Expression of SbLEA3 genes in response to abiotic stresses such as soil moisture deficit (drought), osmotic, salt, and temperature stresses, and exogenous ABA treatments was also studied in the leaves of 2-weeks-old seedlings. ABA and drought induced the expression of all LEA3 genes, while cold and heat stress induced none of them. Promoter analysis revealed the presence of multiple ABRE core cis-elements and a few low temperature response (LTRE)/drought responsive (DRE) cis-elements. This study suggests non-redundant function of LEA3 genes in seed development and stress tolerance in sorghum.