Based on their biological functions in rice or Ruxolitinib other species, the predicted target genes appear to be involved in various bio logical processes. For example, miR159 regulates a MYB gene, which is considered a positive regulator of the GA response during grain maturation. The targets of miR160, Os04g43910 and Os04g59430, are auxin responsive factors, which are important compo nents of auxin signal transduction. MiR444 targeted a type of MADS box transcription factor that is similar to an Arabidopsis homolog that has roles in fruit dehiscence. Moreover, transcription factors, such as NAC do main proteins, growth factors, and the SCARECROW gene regulator, have been observed in other cellular growth developmental processes.
Differential expression of miRNAs and their target genes seem to form a compli cated regulatory network that plays a critical role during grain filling in rice. Discussion Using high throughput sequencing and customized miRNA chips, we analyzed small RNAs in developing transcriptional regulation of the genes involved in grain development. Although a number of studies of small RNAs have been carried out using grains from various developmen tal stages and from various rice accessions, novel miR NAs involved in this process have been continuously discovered. We sequenced small RNA pools from the developing caryopsis of the indica landrace, Baifeng B, at different stages of development and revealed many classes of conserved miRNAs as well as novel ones. The discovery of 11 novel miRNA candidates was supported by detection of corresponding miRNA s that were consistent with recent miRNA criteria for characterization.
No homologous members were reported in other species, indicating that they are prob ably rice specific and found only with extensive tissue sampling. miRNAs have dynamic expression patterns in developing grains Many miRNAs display temporal or tissue specific ex pression patterns. Our sequencing results revealed that more than 100 known rice miRNAs were expressed in the rice grain. Several, such as miR156, miR159, miR164, miR166, miR167 and miR396, were expressed at high levels, indicating that, as they are highly expressed in other tissues such as leaf and root, these conserved miRNAs are possibly important regula tors for rice plant development. Our chip data showed that known and novel miRNAs were expressed differentially during the grain filling process.
Approximately half of the conserved miRNAs detected were up regulated Anacetrapib from 6 to 20 DAF, whereas approximately half were down regulated. Compared with previous reports, the expression levels of most miRNAs were approximately the same or up regulated during the periods 1 5 and 6 10 DAF. Some miRNA genes, such as miR159 and miR399, displayed continu ally high expression levels throughout grain filling.