In this study, we have identified and isolated 126 salinity tolerant cDNAs from the root of a mangrove plant, Bruguiera cylindrica (L.) Blume by using suppression subtractive hybridization (SSH) and bacterial functional screening. Sequencing of 51 subtracted cDNA clones that were differentially expressed in the root of B. cylindrica exposed to 20 parts per thousand (ppt) NaCl water revealed 10 tentative unique genes (TUGs) with putative functions in protein synthesis, storage and destination, metabolism, intracellular trafficking and other functions; and 9 unknown proteins. Meanwhile, the 75 cDNA sequences of B. cylindrica that conferred salinity tolerance to Escherichia coli consisted of 29 TUGs with putative functions in transportation, metabolism and other functions; and 33 with unknown functions. Both approaches yielded 42 unique sequencess that have not been reported else where to be stress related and might provide further understanding of adaptations of this plant to salinity stress.
Salinity is a major abiotic stress that greatly affects plant growth and crop production. Sodium ions in saline soil are toxic to plants because of their adverse effects on potassium nutrition, cytosolic enzyme activities, photosynthesis, and metabolism. It is important to identify genes involved in salinity tolerance from mangrove plants that survive under saline conditions. In this study, a total of 864 randomly selected cDNA clones were isolated and sequenced from the primary cDNA library of Acanthusebracteatus. Among the 521 readable sequences, 138 of them were assembled into 43 contigs, whereas 383 were singletons. Sequence analyses demonstrated that 349 of these expressed sequence tags showed significant homology to functional proteins, of which 18% are particularly interesting as they correspond to genes involved in stress response. Some of these clones, including putative mannitol dehydrogenase, plastidic aldolase, secretory peroxidase, ascorbate peroxidase, and vacuolar H + -ATPase, may be related to osmotic homeostasis, ionic homeostasis, and detoxification.
Salinity reduces plant growth and crop production globally. The discovery of genes in salinity tolerant plants will provide the basis for effective genetic engineering strategies, leading to greater stress tolerance in economically important crops. In this study, we have identified and isolated 107 salinity tolerant candidate genes from a mangrove plant, Acanthus ebracteatus Vahl by using bacterial functional assay. Sequence analysis of these putative salinity tolerant cDNA candidates revealed that 65% of them have not been reported to be stress related and may have great potential for the elucidation of unique salinity tolerant mechanisms in mangrove. Among the genes identified were also genes that had previously been linked to stress response including salinity tolerance, verifying the reliability of this method in isolating salinity tolerant genes by using E. coli as a host.
In this study, we report the sequence, Southern analyses and spatial distribution of four cDNA sequences related to reactive oxygen species (ROS) scavenging systems from a mangrove plant, Acanthus ebracteatus. These four complementary DNA (cDNA) sequences encode cytosolic ascorbate peroxidase (AeAPX), monodehydroascorbate reductase (AeMDHR), glutathione-S-transferase (AeGST), and mitochondrial manganese superoxide dismutase (AeMnSOD), respectively. Experimental results indicated that AeAPX and AeGST belong to multigene families, whereas AeMDHAR and AeMnSOD exhibited substantial differences from other members of the same families. Transcript analyses indicated that all these genes were expressed in flowers. However, only AeAPX, AeMDHAR, and AeMnSOD were expressed in all tissues examined. Although both AeMDHAR and AeMnSOD were highly expressed in flowers, the highest expression of AeMnSOD was in the leaf tissue. The expression of AeMDHAR and AeMnSOD in stem was slightly higher than in the root.AeAPX was expressed at low levels in root and stem tissues and its expression in leaf was slightly higher than in the flower. On the other hand, the transcripts of AeGST were not detected in root and leaf. Its expression was almost equal in stem and flower. The information on spatial distribution and predicted subcellular locations of these antioxidant proteins are important for comprehensive analysis and characterization of ROS scavenging and signaling mechanisms in various plant compartments and tissues.
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