Recently, WRKY transcription factors have also been observed in plants including ferns , mosses , smile mode and the protest.
Wheat and abiotic stress factors
Wheat is one of the main cereal crops used worldwide by humans and animals for many thousands of years along with rice and maize. The annual production of wheat in the world is almost 700 million tons at more than 200 million hectre of area. It is predicted that wheat demand can be increased to 50-70% by 2050. The most widely cultivated wheat types in the modern world are hexaploid bread wheat Triticum aestivum, a hexaploid bread wheat and Triticum durum, a tetraploid wheat. Triticum aestivum is believed to have emerged from the crossing between two interspecies that took place between three distinct diploid species. It is believed that Triticum urartu has a close resemblance with Triticum monococcum and Aegilops speltoides.
Wheat is a light and heat sensitive plant which requires specific environmental condition for its growth. Temperature has a critical and most important role in wheat production. Both the start and end of wheat crop season are limited by certain temperature periods. In the growth season, increase temperature conditions reduce the time period of the plant. Different stages of plant growth are also effected by the changes in temperature resulting in reduce wheat production. Increase temperature during early vegetative phase results in sparse tillering, poor vegetative growth and early heading; and during grain filling phase it leads to forced maturity .
A biotic stress like of water, salt, flooding , low and high temperature and oxidative stress largely affect growth ,development and yield of wheat. It has been predicted that up to 50% of agricultural production can be decreased as a result of abiotic stresses like drought and salinity while biotic stress also cause about 10 to 20% loss in crop productivity. Plants have adapted a series of ways to acclimatize to unfavorable situations. A large number of genes control the feedback mechanism which includes both the metabolic and regulatory proteins. Transcription factors and protein kinases are regulatory proteins which retaliate to stress.
However abiotic and biotic stress factors may cause wheat production loss by 29%. Therefore, new molecular genetic technology and plant gene sequence data have focused on improving tolerant cultivars against environmental stress factors. WRKY transcription factors family is one of the largest transcription factor families across the green lineage.
A number of transcription factors belonging to WRKY family have been recognized in many plants Transcription factors are one of the important tools which can regulate different stress related genes during abiotic stress. A number of transcription factors from various families have been observed to have a role in stress regulation. A transcription factor works by binding with acting sequence of these genes which is mainly present in the promoter region. One transcription factor can These factors actually gives plants an opportunity to respond to a number of abiotic stresses.
WRKY transcription factors
WRKY transcription factors were first identified by Ishiguro and Nakamura in Ipomoea batatas. A number of wrky TFs have been characterized in different plants including rice, cotton, barely parsley, wheat etc .
A WRKY domain comprises of about 60 amino acid in which a conserved sequence WRKYGQK is present. This sequence is followed by a zinc finger motif. In spite of the presence of this conserved region in the domain remaining structure of WRKY factor is highly variable. This WRKY domain of 60 amino acid actually binds to the W box in the promoters of target gene to regulate the transcription.
WRKY transcription factors are classified into 3 groups based on the number and type of the domain.
Group 1 and 2 TFs possess two WRKY domains while transcription factors belonging to group 3 have only 1 domain .C2H2 zinc finger motif is present in group 1 and 2, while in group 3 C2HC motif is present. WRKY TFs can also further classified according to their phylogenetic clades.
The regulatory role of WRKY family in biotic and abiotic stresses has been characterized in plants which include infection of bacteria, fungi, oomycetes and viruses, mechanical stimulation, drought, cold, wounding, high salt and radiation. Most of transcription factors of third group have been involve in plant defense by regulating the signaling pathways .Some other factors also involve in plant development ,embryo development, fruit maturation, maturation of root cells, morphogenesis of trichomes , senescence and dormancy.
Wu and coworker demonstrated in silico cloning to separate complementary DNA of 15 wheat gene which encode the WRKY proteins. Exploration of phylogeny revealed that these genes are associated with major WRKY groups while exploration of expression showed that majority of genes are in leaf but WRKY10 expressed in crown . These genes have role in aging of leaf and abiotic stresses. Any change in the expression of these genes can result in more tendency to endure stress.
Some members of the WRKY family have also identified to have a role in hormone signaling i.e. OSWRKY 71 and 51 which can repress specific signal transduction.
The validation of abiotic stress resistance and different agricultural cultiviars with the help of stress related transcription factor genes can be checked by providing unfavorable and extreme environmental conditions in a particular time period. It is predicted that with more harsh environmental conditions the traits with more tolerance and resistance will be preferred.
Now its time to differentiate between the function of every single stress related transcription factor gene from a number of gene families so that we can regulate biotic and abiotic stress resistance, growth and development and the production of certain crop
sehar nawaz, working in the university of agriculture, Faisalabad.