Background: MADS-box transcription factors, besides being involved in floral organ specification, have also been implicated in several aspects of plant growth and development. In recent years, there have been reports on genomic localization, protein motif structure, phylogenetic relationships, gene structure and expression of the entire MADS-box family in the model plant system, Arabidopsis. Though there have been some studies in rice as well, an analysis of the complete MADS-box family along with a comprehensive expression profiling was still awaited after the completion of rice genome sequencing. Furthermore, owing to the role of MADS-box family in flower development, an analysis involving structure, expression and functional aspects of MADS-box genes in rice and Arabidopsis was required to understand the role of this gene family in reproductive development.

Transcription factors regulate gene expression in response to various external and internal cues by activating or suppressing downstream genes in a pathway. In this study, we provide a complete overview of the genes encoding C(2)H(2) zinc-finger transcription factors in rice, describing the gene structure, gene expression, genome localization, and phylogenetic relationship of each member. The genome of Oryza sativa codes for 189 C(2)H(2) zinc-finger transcription factors, which possess two main types of zinc-fingers (named C and Q). The Q-type zinc fingers contain a conserved motif, QALGGH, and are plant specific, whereas C type zinc fingers are found in other organisms as well. A genome-wide microarray based gene expression analysis involving 14 stages of vegetative and reproductive development along with 3 stress conditions has revealed that C(2)H(2) gene family in indica rice could be involved during all the stages of reproductive development from panicle initiation till seed maturation. A total of 39 genes are up-regulated more than 2-fold, in comparison to vegetative stages, during reproductive development of rice, out of which 18 are specific to panicle development and 12 genes are seed-specific. Twenty-six genes have been found to be up-regulated during three abiotic stresses and of these, 14 genes express specifically during the stress conditions analyzed while 12 are also up-regulated during reproductive development, suggesting that some components of the stress response pathways are also involved in reproduction.

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Identification of genes for quantitative traits is difficult using any single approach due to complex inheritance of the traits and limited resolving power of the individual techniques. Here a combination of genetic mapping and bulked transcriptome profiling was used to narrow down the number of differentially expressed salt-responsive genes in rice in order to identify functional polymorphism of genes underlying the quantitative trait loci (QTL). A population of recombinant inbred lines (RILs) derived from cross between salt-tolerant variety CSR 27 and salt-sensitive variety MI 48 was used to map QTL for salt ion concentrations in different tissues and salt stress susceptibility index (SSI) for spikelet fertility, grain weight, and grain yield. Eight significant QTL intervals were mapped on chromosomes 1, 8, and 12 for the salt ion concentrations and a QTL controlling SSI for spikelet fertility was co-located in one of these intervals on chromosome 8. However, there were total 2,681 genes in these QTL intervals, making it difficult to pinpoint the genes responsible for the functional differences for the traits. Similarly, transcriptome profiling of the seedlings of tolerant and sensitive parents grown under control and salt-stress conditions showed 798 and 2,407 differentially expressed gene probes, respectively. By analyzing pools of RNA extracted from ten each of extremely tolerant and extremely sensitive RILs to normalize the background noise, the number of differentially expressed genes under salt stress was drastically reduced to 30 only. Two of these genes, an integral transmembrane protein DUF6 and a cation chloride cotransporter, were not only co-located in the QTL intervals but also showed the expected distortion of allele frequencies in the extreme tolerant and sensitive RILs, and therefore are suitable for future validation studies and development of functional markers for salt tolerance in rice to facilitate marker-assisted breeding.