Endogenous small RNAs, including microRNAs (miRNAs) and short-interfering RNAs (siRNAs), function as post-transcriptional or transcriptional regulators in plants. miRNA function is essential for normal plant development and therefore is likely to be important in the growth of the rice grain. To investigate the roles of miRNAs in rice grain development, we carried out deep sequencing of the small RNA populations of rice grains at two developmental stages. In a data set of ∼5.5 million sequences, we found representatives of all 20 conserved plant miRNA families. We used an approach based on the presence of miRNA and miRNA* sequences to identify 39 novel, nonconserved rice miRNA families expressed in grains. Cleavage of predicted target mRNAs was confirmed for a number of the new miRNAs. We identified a putative mirtron, indicating that plants may also use spliced introns as a source of miRNAs. We also identified a miRNA-like long hairpin that generates phased 21 nt small RNAs, strongly expressed in developing grains, and show that these small RNAs act in trans to cleave target mRNAs.Comparison of the population of miRNAs and miRNA-like siRNAs in grains to those in other parts of the rice plant reveals that many are expressed in an organ-specific manner.

Condensins are ubiquitously expressed multiprotein complexes that are important for chromosome condensation and epigenetic regulation of gene transcription, but whose specific roles in vertebrates are poorly understood. We describe a mouse strain, nessy, isolated during an ethylnitrosourea screen for recessive immunological mutations. The nessy mouse has a defect in T lymphocyte development that decreases circulating T cell numbers, increases their expression of the activation/memory marker CD44, and dramatically decreases the numbers of CD4 ؉ CD8 ؉ thymocytes and their immediate DN4 precursors. A missense mutation in an unusual alternatively spliced first exon of the kleisin ␤ gene, a member of the condensin II complex, was shown to be responsible and act in a T cell-autonomous manner. Despite the ubiquitous expression and role of condensins, kleisin ␤ nes/nes mice were viable, fertile, and showed no defects even in the parallel pathway of B cell lymphocyte differentiation. These data define a unique lineage-specific requirement for kleisin ␤ in mammalian T cell differentiation.Ncaph2 ͉ splice variation

We investigated the molecular basis of the long-term adaptation to nitrogen (N) limitation of wheat plants grown in a simulated crop canopy, with a focus on the stage when carbon (C) reserves are accumulated in stems for later remobilization to grain. A cDNA microarray representing approximately 36,000 unique sequences was used to compare gene expression in a number of above-ground organs at anthesis. Fructan accumulation in stems was accompanied by elevated transcripts for a suite of fructosyltransferases (FTs) and for a fructan 6-exohydrolase (6-FEH) in the low N compared to high N stems. Clustering analysis identified a grouping that included several FTs and a number of genes thought to be involved in regulation of storage C metabolism or senescence in other systems. Transcripts for three FTs and for 6-FEH increased, while transcripts for 1-FEH decreased, in sucrose-fed wheat stems compared to controls. The opposite trends were seen for these transcripts in wheat stems fed ABA. Of the putative regulators, only transcripts for the WPK4 kinase increased in response to sucrose, suggesting a role for this kinase in C storage metabolism in the reproductive wheat stems grown in low N. This work represents the first large-scale transcriptome study of responses to the most common nutrient limitation in one of the world's most economically important crops.