Endogenous small RNAs function in RNA interference (RNAi) pathways to control gene expression through mRNA cleavage, translational repression, or chromatin modification. Plants and animals contain many microRNAs (miRNAs) that play vital roles in development, including helping to specify cell type and tissue identity. To date, no miRNAs have been reported in unicellular organisms. Here we show that Chlamydomonas reinhardtii, a unicellular green alga, encodes many miRNAs. We also show that a Chlamydomonas miRNA can direct the cleavage of its target mRNA in vivo and in vitro. We further show that the expression of some miRNAs/Candidates increases or decreases during Chlamydomonas gametogenesis. In addition to miRNAs, Chlamydomonas harbors other types of small RNAs including phased small interfering RNAs (siRNAs) that are reminiscent of plant trans-acting siRNAs, as well as siRNAs originating from protein-coding genes and transposons. Our findings suggest that the miRNA pathway and some siRNA pathways are ancient mechanisms of gene regulation that evolved prior to the emergence of multicellularity.[Keywords: Chlamydomonas; miRNA; mRNA cleavage; small RNA; RNAi; RISC] Supplemental material is available at http://www.genesdev.org.

MADS-box genes form a large family of transcription factors and play important roles in flower development and organ differentiation in plants. In this study, 42 wheat cDNAs encoding putative MADS-box genes were isolated. BLASTX searches and phylogenetic analysis indicated that the cDNAs represented 12 of the 14 MADS-box gene subfamilies. TaAGL14 and TaAGL15 formed a new subfamily along with a rice gene OsMADS32. RT-PCR analysis revealed that these genes had different exprsssion patterns in different organs of different stages. Expression patterns of TaAGL1 and TaAGL29 were also determined using in situ hybridization. TaAGL1 was abundantly expressed in primary root tips and the whole spikelet with more intense labeling at lodicules, paleas and stamens. TaAGL29 was expressed in both the non-reproductive parts (lemma, palea and glumes), and stamens and pistils. Moreover, differential expression patterns of these genes were also observed between wheat hybrid and its parents in leaf, stem and root of jointing stage, some were up-regulated while others were down-regulated in hybrid as compared to its parents. We concluded that multiple MADS-box genes exist in wheat genome and are expressed in tissue-specific patterns, and might play important roles in wheat growth and development.

The molecular mechanisms underlying photoperiod or temperature control of flowering time have been recently elucidated, but how plants regulate flowering time in response to other external factors, such as water availability, remains poorly understood. Using a large-scale Hybrid Transcription Factor approach, we identified a bZIP transcriptional factor, O. sativa ABA responsive element binding factor 1 (OsABF1), which acts as a suppressor of floral transition in a photoperiod-independent manner. Simultaneous knockdown of both OsABF1 and its closest homologous gene, OsbZIP40, in rice (Oryza sativa) by RNA interference results in a significantly earlier flowering phenotype. Molecular and genetic analyses demonstrate that a drought regime enhances expression of the OsABF1 gene, which indirectly suppresses expression of the Early heading date 1 (Ehd1) gene that encodes a key activator of rice flowering. Furthermore, we identified a drought-inducible gene named OsWRKY104 that is under the direct regulation of OsABF1. Overexpression of OsWRKY104 can suppress Ehd1 expression and confers a later flowering phenotype in rice. Together, these findings reveal a novel pathway by which rice modulates heading date in response to the change of ambient water availability.Flowering time (or heading date) and drought resistance are two major yield traits in crops, especially rice (Oryza sativa). As global climatic change looms, drought has become the biggest abiotic stress to limit crop yields. Breeders have capitalized on naturally occurring genetic variations to improve or maintain crop yield in times or areas of drought by different strategies (Eisenstein, 2013). Manipulation of floral transition has been a promising way to maximize crop yield during dry periods. This strategy has been successful due to extensive identification of genetic loci and elucidation of molecular mechanisms that control flowering time under diverse or unpredictable environments.Heading date in rice is influenced by many environmental cues such as day length (photoperiod), temperature, nutrition, and water availability. Molecular mechanisms that underlie photoperiod regulation of flowering time have already been characterized, probably because day length is more predictable than other environmental factors during seasonal changes. Rice is a facultative short-day plant that flowers earlier in short days (SDs) than in long days (LDs). Heading date 3a (Hd3a) and RICE FLOWERING LOCUS T1 (RFT1) are two paralogous genes in rice encoding "florigen" molecules expressed in the phloem of leaves and transported to the shoot apical meristem to promote flowering (Tamaki et al., 2007;