Overproduction of the Membrane-bound Receptor-like Protein Kinase 1, RPK1, Enhances Abiotic Stress Tolerance in Arabidopsis

RPK1 (receptor-like protein kinase 1) localizes to the plasma membrane and functions as a regulator of abscisic acid (ABA) signaling in Arabidopsis. In our current study, we investigated the effect of RPK1 disruption and overproduction upon plant responses to drought stress. Transgenic Arabidopsis overexpressing the RPK1 protein showed increased ABA sensitivity in their root growth and stomatal closure and also displayed less transpirational water loss. In contrast, a mutant lacking RPK1 function, rpk1-1, was found to be resistant to ABA during these processes and showed increased water loss. RPK1 overproduction in these transgenic plants thus increased their tolerance to drought stress. We performed microarray analysis of RPK1 transgenic plants and observed enhanced expression of several stress-responsive genes, such as Cor15a, Cor15b, and rd29A, in addition to H₂O₂-responsive genes. Consistently, the expression levels of ABA/stress-responsive genes in rpk1-1 had decreased compared with wild type. The results suggest that the overproduction of RPK1 enhances both the ABA and drought stress signaling pathways. Furthermore, the leaves of the rpk1-1 plants exhibit higher sensitivity to oxidative stress upon ABA-pretreatment, whereas transgenic plants overproducing RPK1 manifest increased tolerance to this stress. Our current data suggest therefore that RPK1 overproduction controls reactive oxygen species homeostasis and enhances both water and oxidative stress tolerance in Arabidopsis.     

Overexpression of Arabidopsis Molybdenum Cofactor Sulfurase Gene Confers Drought Tolerance in Maize (Zea mays L.)

Abscisic acid (ABA) is a key component of the signaling system that integrates plant adaptive responses to abiotic stress. Overexpression of Arabidopsis molybdenum cofactor sulfurase gene (LOS5) in maize markedly enhanced the expression of ZmAO and aldehyde oxidase (AO) activity, leading to ABA accumulation and increased drought tolerance. Transgenic maize (Zea mays L.) exhibited the expected reductions in stomatal aperture, which led to decreased water loss and maintenance of higher relative water content (RWC) and leaf water potential. Also, transgenic maize subjected to drought treatment exhibited lower leaf wilting, electrolyte leakage, malondialdehyde (MDA) and H₂O₂ content, and higher activities of antioxidative enzymes and proline content compared to wild-type (WT) maize. Moreover, overexpression of LOS5 enhanced the expression of stress-regulated genes such as Rad 17, NCED1, CAT1, and ZmP5CS1 under drought stress conditions, and increased root system development and biomass yield after re-watering. The increased drought tolerance in transgenic plants was associated with ABA accumulation via activated AO and expression of stress-related gene via ABA induction, which sequentially induced a set of favorable stress-related physiological and biochemical responses.     

The garlic NF-YC gene, <Emphasis Type="Italic">AsNF-YC8</Emphasis>, positively regulates non-ionic hyperosmotic stress tolerance in tobacco

To investigate the relationship between nuclear factor Y (NF-Y) and stress tolerance in garlic, we cloned a NF-Y family gene AsNF-YC8 from garlic, which was largely upregulated at dehydrate stage. Expression pattern analyses in garlic revealed that AsNF-YC8 is induced through abscisic acid (ABA) and abiotic stresses, such as NaCl and PEG. Compared with wild-type plants, the overexpressing-AsNF-YC8 transgenic tobacco plants showed higher seed germination rates, longer root length and better plant growth under salt and drought stresses. Under drought stress, the transgenic plants maintained higher relative water content (RWC), net photosynthesis, lower levels of malondialdehyde (MDA), and less ion leakage (IL) than wild-type control plants. These results indicate the high tolerance of the transgenic plants to drought stress compared to the WT. The transgenic tobacco lines accumulated less reactive oxygen species (ROS) and exhibited higher antioxidative enzyme activities compared with wild-type (WT) plants under drought stress, which suggested that the overexpression of AsNF-YC8 improves the antioxidant defense system by regulating the activities of these antioxidant enzymes, which in turn protect transgenic lines against drought stress. These results suggest that AsNF-YC8 plays an important role in tolerance to drought and salt stresses.     

siRNA介导的ERA1表达下调对拟南芥抗旱性的影响

ERA1是控制植物气孔开闭的一个重要基因,根据其保守域构建RNA干扰(RNAi)载体并转化拟南芥,考察转基因植株的生长、气孔导度、离体叶片失水率以及ERA1和相关基因表达,探讨siRNA介导的ERA1表达下调对拟南芥抗旱性的影响。结果表明:转基因拟南芥株系中ERA1的表达受到明显抑制,其离体叶片失水率低于野生型,但并未出现ERA1缺失突变体的负面生长表型;转基因株系对ABA处理比野生型更敏感,其ABA处理株的根长显著变短,气孔孔径更小;转基因株ABI1、ABI2、ATHB6的表达量降低,而RAB18、RD29B、ADH1的表达量升高,siRNA介导的ERA1表达下调可能会激活RAB18、RD29B等逆境响应元件。研究发现,采用RNAi技术可以有效下调ERA1表达,在没有过多负面生长表型的前提下提高拟南芥的抗旱性,且ERA1表达下调可能通过ABA途径正面影响拟南芥的抗旱性。     

<Emphasis Type="Italic">SlHDA5</Emphasis>, a Tomato Histone Deacetylase Gene,Is Involved in Responding to Salt,Drought, and ABA

Histone deacetylation catalyzed by histone deacetylases is an important type of histone modification. Histone deacetylases affect various processes of plant development and involve in responding to hormones and biotic and abiotic stresses. Here, we report a tomato PRD3/HDA1 histone deacetylase gene, SlHDA5, which is expressed ubiquitously in different tissues and development stages. Expression profiles in hormone treatments showed that SlHDA5 was induced by abscisic acid (ABA) and methyl jasmonate (MeJA). Seedlings growth of SlHDA5-RNAi lines were more inhibited on the medium containing salt compared with wild type (WT). Under salt stress, chlorophyll in mature leaves degraded earlier in transgenic leaves than that in WT, and transgenic plants displayed wilting earlier and more severe than WT. After drought treatment, transgenic plants wilted and dehydrated earlier than WT, which was confirmed by lower water and chlorophyll content, and higher malondialdehyde (MDA) content in transgenic plants manifesting that the tolerance of transgenic plants to drought receded. Under the treatment of ABA, root length of transgenic seedlings was more strongly repressed by contrast with WT, suggesting repression of SlHDA5 increased seedling sensibility to ABA. Our study indicated that silencing of SlHDA5 resulted in decreasing tolerance to salt, drought, and ABA.     

Functional roles of the pepper antimicrobial protein gene, <Emphasis Type="Italic">CaAMP1</Emphasis>, in abscisic acid signaling,and salt and drought tolerance in <Emphasis Type="Italic">Arabidopsis</Emphasis>

Biotic signaling molecules including abscisic acid (ABA) are involved in signal transduction pathways that mediate the defense response of plants to environmental stresses. The antimicrobial protein gene CaAMP1, previously isolated from pepper (Capsicum annuum), was strongly induced in pepper leaves exposed to ABA, NaCl, drought, or low temperature. Because transformation is very difficult in pepper, we overexpressed CaAMP1 in Arabidopsis. CaAMP1-overexpressing (OX) transgenic plants exhibited reduced sensitivity to ABA during the seed germination and seedling stages. Overexpression of CaAMP1 conferred enhanced tolerance to high salinity and drought, accompanied by altered expression of the AtRD29A gene, which is correlated with ABA levels and environmental stresses. The transgenic plants were also highly tolerant to osmotic stress caused by high concentrations of mannitol. Together, these results suggest that overexpression of the CaAMP1 transgene modulates salt and drought tolerance in Arabidopsis through ABA-mediated cell signaling. The nucleotide sequence data reported here have been deposited in the GenBank database under the accession number AY548741.