F-box proteins constitute a large family in eukaryotes and are characterized by a conserved F-box motif (approximately 40 amino acids). As components of the Skp1p-cullin-F-box complex, F-box proteins are critical for the controlled degradation of cellular proteins. We have identified 687 potential F-box proteins in rice (Oryza sativa), the model monocotyledonous plant, by a reiterative database search. Computational analysis revealed the presence of several other functional domains, including leucine-rich repeats, kelch repeats, F-box associated domain, domain of unknown function, and tubby domain in F-box proteins. Based upon their domain composition, they have been classified into 10 subfamilies. Several putative novel conserved motifs have been identified in F-box proteins, which do not contain any other known functional domain. An analysis of a complete set of F-box proteins in rice is presented, including classification, chromosomal location, conserved motifs, and phylogenetic relationship. It appears that the expansion of F-box family in rice, in large part, might have occurred due to localized gene duplications. Furthermore, comprehensive digital expression analysis of F-box protein-encoding genes has been complemented with microarray analysis. The results reveal specific and/or overlapping expression of rice F-box protein-encoding genes during floral transition as well as panicle and seed development. At least 43 F-box protein-encoding genes have been found to be differentially expressed in rice seedlings subjected to different abiotic stress conditions. The expression of several F-box protein-encoding genes is also influenced by light. The structure and function of F-box proteins in plants is discussed in light of these results and the published information. These data will be useful for prioritization of F-box proteins for functional validation in rice.

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. Results: A genome-wide molecular characterization and microarray-based expression profiling of the genes encoding MADS-box transcription factor family in rice is presented. Using a thorough annotation exercise, 75 MADS-box genes have been identified in rice and categorized into MIKC^c, MIKC*, Mα, Mβ and Mγ groups based on phylogeny. Chromosomal localization of these genes reveals that 16 MADS-box genes, mostly MIKC^c-type, are located within the duplicated segments of the rice genome, whereas most of the M-type genes, 20 in all, seem to have resulted from tandem duplications. Nine members belonging to the Mβ group, which was considered absent in monocots, have also been identified. The expression profiles of all the MADS-box genes have been analyzed under 11 temporal stages of panicle and seed development, three abiotic stress conditions, along with three stages of vegetative development. Transcripts for 31 genes accumulate preferentially in the reproductive phase, of which, 12 genes are specifically expressed in seeds, and six genes show expression specific to panicle development. Differential expression of seven genes under stress conditions is also evident. An attempt has been made to gain insight into plausible functions of rice MADS-box genes by collating the expression data of functionally validated genes in rice and Arabidopsis. Conclusion: Only a limited number of MADS genes have been functionally validated in rice. A comprehensive annotation and transcriptome profiling undertaken in this investigation adds to our understanding of the involvement of MADS-box family genes during reproductive development and stress in rice and also provides the basis for selection of candidate genes for functional validation studies.

Important developmental processes in both plants and animals are partly regulated by genes whose expression is modulated at the post-transcriptional level by processes such as RNA interference (RNAi). Dicers, Argonautes and RNA-dependent RNA polymerases (RDR) form the core components that facilitate gene silencing and have been implicated in the initiation and maintenance of the trigger RNA molecules, central to process of RNAi. Investigations in eukaryotes have revealed that these proteins are encoded by variable number of genes with plants showing relatively higher number in each gene family. To date, no systematic expression profiling of these genes in any of the organisms has been reported.

Receptor-like cytoplasmic kinases (RLCKs) in plants belong to the super family of receptor-like kinases (RLKs). These proteins show homology to RLKs in kinase domain but lack the transmembrane domain. Some of the functionally characterized RLCKs from plants have been shown to play roles in development and stress responses. Previously, 149 and 187 RLCK encoding genes were identified from Arabidopsis and rice, respectively. By using HMM-based domain structure and phylogenetic relationships, we have identified 379 OsRLCKs from rice. OsRLCKs are distributed on all 12 chromosomes of rice and some members are located on duplicated chromosomal segments. Several OsRLCKs probably also undergo alternative splicing, some having evidence only in the form of gene models. To understand their possible functions, expression patterns during landmark stages of vegetative and reproductive development as well as abiotic and biotic stress using microarray and MPSS-based data were analyzed. Real-time PCR-based expression profiling for a selected few genes confirmed the outcome of microarray analysis. Differential expression patterns observed for majority of OsRLCKs during development and stress suggest their involvement in diverse functions in rice. Majority of the stress-responsive OsRLCKs were also found to be localized within mapped regions of abiotic stress QTLs. Outcome of this study would help in selecting organ/development stage specific OsRLCK genes/targets for functional validation studies.