Study On The Expression Profiles Of Salt Responsive Transcripts In Maize Seedlings

Salt stress is one of the most serious abiotic stresses threaten the crop plants worldwide. High salinity causes serious damage to crop growth, resulting in lower quality and less yield. To survive under high salinity condition in their rooted lifestyle, crop plants have evolved a considerable degree of developmental plasticity, many genes change their expression profiles, which are involved in a broad spectrum of biochemical, cellular, and physiological processes. To cope with both ironic and osmotic stresses introduced by salt, many functional and regulating genes, including those involved in the cell detoxification, membrane transporting, energy maintaining, protein processing, and phytohormone responding, changed their expression profiles. In addition, these functional genes were regulated at different levels, such as the stress transduction cascades, which regulating gene expression at transcriptional level; miRNA dependent post transcriptional gene silencing were also involved in plant salt stress response .Maize (Zea mays L.) is one of the most important cereal crops in the world, it provides not only food and feed, but also material for bio-ethanol production, it is a crop that combined food, feed and fuel in one. Maize is salt-sensitive, and the salt sensitivities were distinct between maize inbred lines.Two maize inbred lines NC286 and Huangzao4 were selected with distinct salt stress sensitivity, SSH and cDNA chip hybridizing were processed between the salt stressed and un-stressed control materials. Differently expressed ESTs were detected. These ESTs were considered to be salt stress responsive ones, which involved in a vast spectrum of cellular and physiological processes.This research aimed in clarifies the genetic mechanisms of maize salt stress responsive and elucidates the relationship between differently expressed ESTs and distinct salt stress sensitivity. The main results derived from the high throughput methods were listed as following.1. Many protein kinase transcripts were differently regulated under salt stress, and the protein phosphatase transcripts were up-regulated, hinted that the reversible protein phosphorylation may play roles in salt stress signal cascades.2. Transcriptional and translational regulations occurred under salt shock.3. UB/26S mechanism was much more active under salt stress condition than in un-stressed control, which may resulted from the increasing of destroyed proteins. At the same time, activation of the protein degradation system may also enhance the re-use of amino acids.4. Salt stress may destroy the photosynthesis system, which in turn affect the energy supplement.5. Most of the histones and ribosomal proteins transcripts were repressed under salt stress, which may influence the repression of gene transcription and protein translation.6. Most of the ESTs encoding cellular framework proteins were repressed under salt shock.7. Most of the ESTs associated with membrane trafficking were detected to be up-regulated by the salt stress, which may play roles in re-establishing of homeostasis.In all, there are 8 co-detected ESTs from the SSH and cDNA chip. Expression profiles of these 8 ESTs under salt, dehydration and chilling stress were established. For most of the ESTs, the expression profiles under salt and dehydration stress were of the same, yet they were differing from those under chilling stress.Corn responds to salt stress via changes in gene expression, metabolism, and physiology. This adaptation is achieved through the regulation of gene expression at transcriptional and post-transcriptional levels. microRNAs (miRNAs) have been found to act as key regulating factors at post-transcriptional levels. However, little is known about the role of miRNAs in plants' responses to salt stress.A customμParaflo^TM microfluidic array (LC science USA) containing Release version 10.1 plant miRNA probes (http://microrna.sanger.ac.uk/) was used to discover salt stress responsive miRNAs using the differences in miRNAs expression between the salt-tolerant maize inbred line NC286 and the salt-sensitive maize line Huangzao4.Salt responsive miRNAs are involved in the regulation of metabolic, morphological and physiological adaptations of maize seedlings at the post-transcriptional level. The miRNA genotype-specific expression model might explain the distinct salt sensitivities between maize lines.miRNA microarray hybridization revealed that a total of 98 miRNAs, from 27 plant miRNA families, had significantly altered expression after salt treatment. These microRNAs displayed different expression profiles under salt stress, and miRNAs belonging to the same miRNA family showed the same behaviour. Interestingly, we found 18 miRNAs were only expressed in the salt tolerant maize line NC286, and 25 miRNAs showed a delayed regulating pattern in the salt sensitive line.For all the salt responsive ESTs and miRNA genes, the key stress related cis-elements in their promoter regions were predicted. The results showed that the most frequently detected stress related cis-elements ABRE, ARE and MYBs were of the same in saltresponsive ESTs and miRNA genes, suggesting that the salt stress responsive coding andnon-coding genes were regulated by the same up steam factors.