Genomic identification of group A bZIP transcription factors and their responses to abiotic stress in carrot.

The basic-region/leucine-zipper (bZIP) family is one of the major transcription factor (TF) families associated with responses to abiotic stresses. Many members of group A in this family have been extensively examined and are reported to perform significant functions in ABA signaling as well as in responses to abiotic stresses. In this study, 10 bZIP factors in carrot were classified into group A based on their DNA-binding domains. The cis-acting regulatory elements and folding states of these 10 factors were analyzed. Evolutionary analysis of the group A members suggested their importance during the course of evolution in plants. In addition, cis-acting elements and the folding state of proteins were important for DNA binding and could affect gene expression. Quantitative RT-PCR was conducted to investigate the stress response of 10 genes encoding the group A factors. Six genes showed responses to abiotic stresses, while four genes showed other special phenomenon. The current analysis on group A bZIP family TFs in carrot is the first to investigate the TFs of Apiaceae via genome analysis. These results provide new information for future studies on carrot.

Structural and physiological characterization during wheat pericarp development.

KEY MESSAGE: The cytological and physiological features of developing wheat pericarp were clearly characterized in this report. Our results may be helpful to articulate the functions of pericarp during the seed development. Although wheat pericarp has been well studied, knowledge of the sequence of events in the process of pericarp development is incomplete. In the present study, the structural development process of wheat (Triticum aestivum L.) pericarp was investigated in detail using resin microtomy and microscopy. Chlorophyll contents, and photosynthetic and respiratory rates, in pericarp were determined using spectrophotometer and an oxygen electrode, respectively. Mineral nutrient contents were also determined using scanning electron microscopy. The main results are as follows: (1) based on the structures and physiological characteristics observed, the developmental process of pericarp was divided into four stages, growth, formation, extinction and maturation stages, pericarp exhibited specific features at each stage. (2) Pericarp development differed in different parts, or varieties, of wheat. The dorsal pericarp had fewer starch grains and slower rates of apoptosis than the abdominal mesocarp. The cross cells in dorsal pericarp had an irregular outline. When compared with soft wheat cv. Yangmai 11, mesocarp cells in hard wheat cv. Xumai 30 had more starch grains, larger cell size and longer development duration. (3) The chlorophyll content, photosynthesis rate and respiratory rate in pericarp increased gradually, reaching a maximum about 16 days after anthesis, and later decreased continually. The photosynthetic rate in pericarp was lower than the respiration rate. (4) The contents of mineral elements in pericarp, such as calcium, zinc, iron and potassium were higher than those in the inner endosperm. The data indicate that wheat pericarp has many functions, e.g. protection, photosynthesis, mineral accumulation, synthesis and degradation of starch.

High level expression of a recombinant acid phytase gene in Pichia pastoris.

AIMS: To achieve high phytase yield with improved enzymatic activity in Pichia pastoris. METHODS AND RESULTS: The 1347-bp phytase gene of Aspergillus niger SK-57 was synthesized using a successive polymerase chain reaction and was altered by deleting intronic sequences, optimizing codon usage and replacing its original signal sequence with a synthetic signal peptide (designated MF4I) that is a codon-modified Saccharomyces cerevisiae mating factor alpha-prepro-leader sequence. The gene constructs containing wild type or modified phytase gene coding sequences under the control of the highly-inducible alcohol oxidase gene promoter with the MF4I- or wild type alpha-signal sequence were used to transform Pichia pastoris. The P. pastoris strain that expressed the modified phytase gene (phyA-sh) with MF4I sequence produced 6.1 g purified phytase per litre of culture fluid, with the phytase activity of 865 U ml(-1). The expressed phytase varied in size (64, 67, 87, 110 and 120 kDa), but could be deglycosylated to produce a homogeneous 64 kDa protein. The recombinant phytase had two pH optima (pH 2.5 and pH 5.5) and an optimum temperature of 60 degrees C. CONCLUSIONS: The P. pastoris strain with the genetically engineered phytase gene produced 6.1 g l(-1) of phytase or 865 U ml(-1) phytase activity, a 14.5-fold increase compared with the P. pastoris strain with the wild type phytase gene. SIGNIFICANCE AND IMPACT OF THE STUDY: The P. pastoris strain expressing the modified phytase gene with the MF4I signal peptide showed great potential as a commercial phytase production system.