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Ethylene plays an important role in the regulation of many growth and developmental processes of higher plants. In tomato, Le-ACS6, a member of the ACC synthase multigene family involved in system 1 ethylene biosynthesis during fruit ripening, is subject to negative feedback regulation by ethylene. To identify the cis-elements that are responsible for the negative feedback control, we established an in vitro transient assay system employing particle bombardment on mature-green tomato fruit pericarp to examine the expression of a luciferase (LUC) reporter gene driven by a 5'-serially deleted Le-ACS6 promoter. The results localized putative cis-elements required for negative ethylene-response between -347 and -266 upstream from the translational start site ATG. Several lines of stable transformation of the Le-ACS6 promoter and GUS reporter fusion gene containing internal deletion from -347 to -266 were generated. The expression pattern of the GUS reporter showed that removal of the nucleotides from -347 to -266 completely eliminated the response of the Le-ACS6 promoter to exogenous ethylene. [ABSTRACT FROM AUTHOR]

Abstract The full length cDNA coding for a novel vacuolar Na+/H+ antiporter (GmNHX1) was cloned from soybean and determined to consist of 2591 bp with a 5′-untranslated region of 464 bp, an open reading frame (ORF) of 1641 bp, and a 3′-untranslated region of 466 bp. The deduced protein sequence contains 546 aa with the typical characters of the vacuolar Na+/H+ antiporters, and shares high similarity with that of AtNHX1, OsNHX1 and AgNHX1. The soybean genome showed a single copy of the GmNHX1 gene. Northern blot analysis demonstrated that the expression of the GmNHX1 was tissue-specific, increased by ABA treatment, NaCl, KCl, LiCl and dehydration stress, and lower in leaves but higher in roots and hypocotyls of salt-tolerant than salt-sensitive cultivars. The GmNHX1 was overexpressed under the control of a tandem cauliflower mosaic virus (CaMV) 35S promoter in the model leguminous plant Lotus corniculatus L. and conferred salt-tolerance of the transgenic plants. Measurements of Na+ and K+ contents in both roots and shoots demonstrated that the plantlets of GmNHX1-overexpressing lines had lower Na+ and K+ content, and higher K+/Na+ ratio than the controlled lines that were transformed with the empty vector, which indicates that the salt-tolerance conferred by GmNHX1 is closely related with decreased accumulation of Na+ in the transgenic plants. [ABSTRACT FROM AUTHOR]

Maize Lis1 (lethal leaf-spot 1) gene and its Arabidopsis orthologue AtAcd1 have been suggested to encode pheide a oxygenase (PaO), a key enzyme catalyzing chlorophyll breakdown. To further elucidate the molecular mechanism that regulates chlorophyll catabolism during soybean leaf senescence, a soybean Lis1 homolog was cloned and designated as GmLis1 (GenBank Accession No. DQ154009). Database searches using the deduced protein sequence revealed that it was highly homologous to Lis1 genes or Lis1 orthologues in Arabidopsis, maize, cowpea and tomato. Structural analysis of the predicted GmLLS1 protein revealed typical Rieske [2Fe-2S] and mononuclear iron-binding domains as well as the C-terminus CxxC motif that were conserved in and featured PaO homologues. RT-PCR results showed that the transcription of GmLis1 was up-regulated in all the three tested senescence systems: the natural leaf senescence process, the dark-induced primary leaf senescence and senescing cotyledons. We have previously described the involvement of an LRR receptor-like kinase (RLK), RLPK2 in regulation of soybean leaf senescence. Here we report that the expression of GmLis1 gene was dramatically down-regulated by the RNAi-mediated suppression of rlpk2 and, as expected, greatly up regulated by the CaMV 35S promoter derived overexpression of this RLK gene. These results suggested that the expression of GmLis1 was controlled by the RLPK2-mediated senescence signaling pathway. The observation that the detached rlpk2-RNAi transgenic leaves exhibited light-dependent necrotic lesions, which featured the [ABSTRACT FROM AUTHOR]

Leaf senescence that occurs in the last stage of left development is a genetically programmed process. It is very significant to elucidate the molecular mechanisms that control the initiation and progression of leaf senescence and the way the senescence signal is transduced. In a previous study an artificially induced soybean leaf senescence, we cloned a novel gene designated rlpk2 (Genbank Accession No. AY687391) that encodes a leucine-rich repeat (LRR) receptor like protein kinase. The expression level of rlpk2 gene was shown to he strongly up-regulated during both the natural leaf senescence process in this report and the artificially induced primary-leaf-senescence process in our previous work. The RNA interference (RNAi)-mediated knocking-down of rlpk2 dramatically retarded both the natural and nutrient deficiency-induced leaf senescence in transgenic soybean. The transgenic leaves showed more cell-aggregated surface structure and higher content of chlorophyll. [ABSTRACT FROM AUTHOR]