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OsNAC45 belongs to the NAC family of (for NAM/ATAF1/2/CUC2) transcription factors, which play an important role in plant development and abiotic stress responses. Transgenic rice plants overexpressing OsNAC45 have exhibited improved tolerance to salt and drought stress. This study aimed to investigate the mechanism underlying the effects of OsNAC45 on root development under abiotic stress in rice Zhonghua11 (ZH11) (Oryza sativa L.). The OsNAC45 GUS expression was strong in roots of the adult stage, weak in the seedling stage, and induced by low-temperature stress in the seedling stage. Under NaCl and low temperature stress, the OsNAC45 overexpression (OE) lines exhibited maintenance of root structure and normal growth of the seedling root, but the RNAi lines of OsNAC45 were more sensitive. The roots of the OE lines accumulated less superoxide anion under low temperature stress and more hydrogen peroxide under normal conditions than WT. After NaCl treatment, the Peroxidase (POD) assay showed POD activity of the roots in OE lines were elevated, but were decreased in RNAi lines and WT; additionally, the increment of lignin content in OE lines was significantly higher than RNAi lines and WT in roots. Furthermore, expression levels of some rice root development-related genes were altered in the transgenic plants. Under cold and salt stresses, expression of NCED4, a key enzyme in abscisic acid synthesis, was decreased in OE lines and raised in RNAi lines compared to WT. The data suggests that OsNAC45 may participate in the response of cold/salt stresses by lessening the accumulation of reactive oxygen species and increasing lignin in rice roots thus alleviating the restraint to the growth of seedling root. Overexpression of OsNAC45 weakened the high temperature tolerance; however, inhibiting its expression could improve the tolerance. Together, these results indicate that OsNAC45 plays an important role in the coordination, development, and response of rice plants under abiotic stresses.

The mitogen-activated protein kinase kinases (MKK) represent a small gene family that is located at the center of the MAPK cascade and play an important role in responses to biotic and abiotic stresses and in plant growth and development. Here, we report the cloning of an MKK gene from Brassica napus, BnMKK1 (GenBank Accession No. HQ916282), by RT-PCR. The BnMKK1 cDNA is 1,447 bp in length with an open reading frame of 1,092 bp. The gene encodes a putative MKK protein that contains a conserved motif S/TxxxxxS/T (where x represents any amino acid) and a MPK docking domain in its N-terminal extension. The orthologues of the BnMKK1 protein are highly conserved among mosses, ferns, dicotyledons and monocotyledons. Southern hybridization revealed the presence of more than two copies of the BnMKK1 homologues in the genome of B. napus. Quantitative reverse transcription–polymerase chain reaction analyses showed that the BnMKK1 transcripts accumulated in response to cold, ABA (abscisic acid) and MeJA (methyl jasmonate) but declined in response to mannitol, NaCl, H2O2, and SA (salicylic acid). The inhibitors of MAPK activation, PD98059 and U0126, did not inhibit BnMKK1 transcription. BnMKK1 transgenic tobacco plants grew slower and showed significantly delayed flower times compared to the wild type. Their root development was insensitive to treatment with 100 mM IAA (indole-3-acetic acid). The detached leaves from the transgenic BnMKK1 tobacco plants strengthened the inhibition to bacterial development at later growth stages. The overexpression of BnMKK1 leads to rapid water loss and enhanced sensitivities to drought stress in transgenic tobacco plants. These results show that BnMKK1 plays an important role in the response of plants to pathogenic bacteria and drought stress.

A novel gene, OsAHL1, containing an AT-hook motif and a PPC domain was identified through genome-wide profiling and analysis of mRNAs by comparing the microarray of drought-challenged versus normally watered rice. The results indicated OsAHL1 has both drought avoidance and drought tolerance that could greatly improve drought resistance of the rice plant. Overexpression of OsAHL1 enhanced multiple stress tolerances in rice plants during both seedling and panicle development stages. Functional studies revealed that OsAHL1 regulates root development under drought condition to enhance drought avoidance, participates in oxidative stress response and also regulates the content of chlorophyll in rice leaves. OsAHL1 specifically binds to the A/T rich sequence region of promoters or introns and hence directly regulates the expression of many stress related downstream genes.

Pyridoxal kinase is key enzyme for the biosynthesis of pyridoxal 5'-phosphate, the biologically active form of vitamin B6, in the salvage pathway. A pyridoxal kinase gene, BnPKL (GenBank accession No. DQ463962), was isolated from oilseed rape (Brassica napus L.) following water stress through rapid amplification of complementary DNA (cDNA) ends. The results showed that the gene had two splice variants: PKL and PKL2. PKL, the long cDNA, encodes a 334 amino acid protein with a complete ATP-binding site, pyridoxal kinase-binding site and dimer interface site of a pyridoxal kinase, while PKL2, the short cDNA, lacked a partial domain. Southern blot showed that there were two copies in Brassica napus. The expression of BnPKL cDNA could rescue the mutant phenotype of Escherichia coli defective in pyridoxal kinase. Real-time reverse transcription-polymerase chain reaction revealed that the relative abundance of two transcripts are modulated by development and environmental stresses. Abscisic acid and NaCl were inclined to decrease PKL expression, but H2O2 and cold temperatures induced the PKL expression. In addition, the PKL expression could be transiently induced by jasmonate acid at an early stage, abscisic acid, salicylic acid and jasmonate acid enhanced the PKL expression in roots. Our results demonstrated that BnPKL was a pyridoxal kinase involved in responses to biotic and abiotic stresses.

A computer-based analysis was conducted to assess the characteristics of amino acid repeats in Arabidopsis and rice. Our analysis showed a negative gradient in amino acid repeat distribution along the direction of translation in plants. Repeat occurrences are obviously associated with position in plant proteins but are not consistent with the corresponding amino acid contents. These repeats are encoded by the mixed synonymous codons rather than the uninterrupted reiterations of a single codon, and both Arabidopsis and rice have gradients in their distribution. Functional investigation showed that these repeat-containing proteins are preferentially involved in transcription regulation and protein ubiquitination but significantly underrepresented in the processes of DNA recombination and DNA replication. These data reveal that the direction-related mutation bias and functional selection have influenced the distribution of amino acid repeats in plants.Key words: amino acid repeats, amino acid usage, distributional gradient, regulation of transcription, protein ubiquitination.

A gene encoding mitogen-activated protein kinase was isolated from oilseed rape (Brassica napus) following drought treatment. The cloned gene, designated as BnMPK3 (GenBank accession no. AY642433 ), contains one phosphorylation motif (TEY) and a conserved CD domain in its C-terminal extension. BnMPK3 is highly homologous to AtMPK3 gene from Arabidopsis thaliana and belongs to the A-subgroup of mitogen-activated protein kinase. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) analyses showed that the expression level of BnMPK3 transcript was up-regulated by mannitol, NaCl, cold, H2O2, abscisic acid (ABA), salicylic acid (SA) and methyl jasmonate acid (m-JA). Interestingly, SA, m-JA enhanced gradually BnMPK3's expression all along after 20–60 min treatment, but its expression was all initiated by mannitol, NaCl, H2O2 and ABA in a short time and reached the highest level after 1–2 h treatment. Hysteresis of cold response showed that BnMPK3's expression was initiated after 1 h from normal growth conditions at room temperature to 4 °C, and reached the highest level after 6 h treatment. The inhibitors of MAPK activation PD98059 and U0126 did not inhibit BnMPK3 transcript. BnMPK3 was cloned into pYES2.1 and transformed into yeasts, and BnMPK3's expression enhanced yeasts’ resistance to mannitol and peroxide in 600 mM mannitol and 0.2 mM tBuOOH drug assays. The present studies show that BnMPK3 is an early response gene involved in responses to biotic and abiotic stresses.

A fluorescencein situ hybridization (FISH) procedure was adopted to physically map two rice BAC clones 24E21 and 4F22 linked toGm-6 andPi-5(t) inO. officinalis. FISH results showed that the two BAC clones were located at 4L. The percentage distance from the centromere to the hybridization sites was 72±2.62 for 24E21 and 54±5.43 for 4F22, the detection rates were 52.70% and 61.2%. The results obtained from the BAC and plasmid clones, RG214 and RZ565 of cultivated rice andO. officinalis were the same. This suggested that the markers, RG214 and RZ565 of cultivated rice andO. officinalis were in the same BAC clones. The homologous sequences ofGm-6 andPi-5(t) inO. officinalis were positions that signals existed on the 4L. Many signals were observed when no Cot-1 DNA blocked. This also showed that repetitive sequences were some homolgous between cultivated rice andO. officinalis. The identification of chromosome 4 ofO. officinalis is based on Jena et al. (1994). In our study, we discussed the possibility of physical map inO. officinalis with rice BAC clones.

Plant heat shock proteins (Hsps) facilitate protein folding or assembly under diverse developmental and adverse environmental conditions. Nine OsHsps were identified in our previous study from a proteomic analysis of rice cv. IRAT 109 leaf samples at the seedling stage under drought stress. To obtain additional information on the 9 OsHsp genes, this study focused on an expression profile analysis at different development stages throughout the life cycle of rice, and under different abiotic stresses and phytohormone treatments. The 9 genes exhibited distinctive expression patterns in different organs or development stages. Five of the genes (OsHsp72.90, OsHsp72.57, OsHsp71.18, OsHsp24.15 and OsHsp18.03) showed high expression in the endosperm, indicating that OsHsp genes may play important roles in rice seed development. All 9 OsHsps were up-regulated under heat, polyethylene glycol, and abscisic acid treatment, whereas salt stress caused up-regulation of 6 genes (OsHsp93.04, OsHsp71.10, OsHsp71.18, OsHsp72.57, OsHsp24.15 and OsHsp18.03) and cold stress resulted in down-regulation of OsHsp93.04 and OsHsp72.57. These diverse expression profiles imply potential functional diversity of the Hsp gene family in rice.