The chenopodiaceae Suaeda salsa L. is a leaf succulent euhalophyte. Shoots of the S. salsa are larger and more succulent when grown in highly saline environments. This increased growth and water uptake has been correlated with a large and specific cellular accumulation of sodium. S. salsa does not have salt glands or salt bladders on its leaves. Thus, this plant must compartmentalize the toxic Na(+) in the vacuoles. The ability to compartmentalize sodium may result from a stimulation of the proton pumps that provide the driving force for increased sodium transport into the vacuole. In this work, we isolated the cDNA of the vacuolar membrane proton-translocating inorganic pyrophosphatase (H(+) -PPase) from S. salsa. The SsVP cDNA contains an uninterrupted open reading frame of 2292 bp, coding for a polypeptide of 764 amino acids. Northern blotting analysis showed that SsVP was induced in salinity treated leaves. The activities of both the V-ATPase and the V-PPase in Arabidopsis overexpressing SsVP-2 is higher markedly than in wild-type plant under 200 mM NaCl and drought stresses. The Overexpression of SsVP can increase salt and drought tolerance of transgenic Arabidopsis.

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The halophyteLimonium sinenseKuntze is used in traditional Chinese medicine for clearing heat and for detoxification. To examine the detoxification and salt-tolerance mechanisms of this plant, we analyzed antioxidant enzyme activities and transcript levels of genes encoding antioxidant enzymes inL. sinenseseedlings under salt stress (500 mmol/L NaCl). Catalase showed the largest increase in activity, peaking on day 4 of the 7-day NaCl treatment. Peroxidase and superoxide dismutase activities also increased, peaking on days 2 and 3 of the NaCl treatment, respectively. The activities of antioxidant enzymes decreased as the duration of the NaCl treatment extended. The transcript levels of genes encoding antioxidant enzymes were upregulated under NaCl stress. The peak in theLsCATtranscript level was earlier than the peaks inLsAPXandLsGPXtranscript levels. The malondialdehyde content only slightly increased inL. sinenseseedlings under NaCl stress. This was indicative of a low level of lipid peroxidation, consistent with the increased antioxidant enzyme activities and gene transcript levels. These results show that, under NaCl stress, the antioxidant system ofL. sinenseis activated and effectively scavenges reactive oxygen species. This reduces oxidative damage and allows the plant to maintain growth under NaCl stress.

Several MYB transcription factors are known to play important roles in plant resistance to environmental stressors. However, the mechanism governing the involvement of MYBs in regulating tobacco mosaic virus (TMV) resistance in plants is still unclear. In this study, we found that not only is Nicotiana benthamiana MYB4-like involved in defence against TMV, but also that the ethylene pathway participates in MYB4L-mediated resistance. Transcription of NbMYB4L was up-regulated in N. benthamiana infected with TMV. Silencing of NbMYB4L led to intensified TMV replication, whereas overexpression of NbMYB4L induced significant resistance to TMV. Transcription of NbMYB4L was greater in 1-aminocyclopropanecarboxylic acid (ACC, ethylene precursor)pretreated plants but lower when the ethylene signalling pathway was blocked during TMV infection. Gene expression analysis showed that the transcription of NbMYB4L was largely suppressed in ETHYLENE INSENSITIVE 3-like 1(EIL1)-silenced plants. The results of electrophoretic mobility shift assay and chromatin immunoprecipitationquantitative PCR (ChIP-qPCR) experiments indicated that NbEIL1 could directly bind to two specific regions of the NbMYB4L promoter. Furthermore, a luciferase assay revealed that NbEIL1 significantly induced the reporter activity of the MYB4L promoter in N. benthamiana. These results point to NbEIL1 functioning as a positive regulator of NbMYB4L transcription in N. benthamiana against TMV. Collectively, our work reveals that EIL1 and MYB4L constitute a coherent feed-forward loop involved in the robust regulation of resistance to TMV in N. benthamiana.