**1.4. Small RNA regulation of seed composition**

Small RNAs, such as miRNAs and short interfering RNAs (siRNAs), are key components of the evolutionarily conserved system of gene regulation in eukaryotes [166]. Wherein, microR-NAs (miRNAs) are a class of non-coding small RNAs of 20–24 nt in length that play an important role in plant growth and development. Structurally, except for the characteristics of the segments, all miRNA precursors have well-predicted stem-loop hairpin structures, and this fold-back hairpin structure has a low degree of freedom of energy [167]. The microRNA database (http://www.mirbase.org/) is a searchable database of published miRNA sequences and annotations. According to miRBase, miRNA information of 1269 species has been collected, including 399 soybean miRNAs. For example, gma-MIR156d belongs to the MIPF0000008, MIR156 gene family, described as *Glycine max* miR156d stem-loop, annotated that microRNA (miRNA) precursor mir-156 is a family of plant non-coding RNA. This microRNA has now been predicted or experimentally confirmed in a range of plant species (MIPF0000008). The products are thought to have regulatory roles through complementarity to mRNA. SFGD is a comprehensive database of integrated genomic and transcriptome data and a comprehensive database of soy acyl lipid metabolic pathways, including a coexpression regulatory network of 23,267 genes and 1873 miRNA-target pairs as well as a set of acyl-lipid pathways containing 221 enzymes and more than 1550 genes, providing biologists with a useful toolbox [168]. In addition, SoyKB is also a website, which provides information on soybean genomics, transcriptomics, proteomics and metabolomics as well as gene function and biology annotation, including information like genes, microRNAs, metabolites and mono nucleotide polymorphisms (SNPs) [169]. Shi and Chiang used miRNA-specific forward primers and sequences complementary to poly(T) linkers as reverse primers to find a simple and effective method to determine miRNA expression. Total RNA (including miRNAs) was polyadenylated and reverse transcribed into cDNA using poly (T) linkers for real-time PCR.

There are few studies on miRNAs related to plant quality. Soybean cotyledons affect soybean seed yield and quality. Goettel et al. analyzed 304 miRNA genes expressed in soybean cotyledons and predicted their complex miRNA networks to 1910 genes. By analyzing extensive biological pathways present in soybean cotyledons, the evolutionary pathways of soybean miR15/49 in soybean cotyledons were further demonstrated [170]. Ye et al. identified and analyzed the whole genome of miRNA endogenous target gene mimic (eTM) and the phagemid-generated siRNA (PHAS) in soybean, with a focus on lipid metabolismrelated genes. Lipid metabolism was found to be regulated by a potentially complex noncoding network in soybean, of which 28 may be miRNA-regulated and nine may be further regulated [171].
