Auxin regulates cell division and elongation of the primordial cells through its concentration and then shaped the plant architecture.  Cell division and elongation form the internode of soybean and result in different plant heights and lodging resistance.  Yet the mechanisms behind are unclear in soybean.  To elucidate the mechanism of the concentration difference of auxin related to stem development in soybean, samples of apical shoot, elongation zone, and mature zone from the developing stems of soybean seedlings, Charleston, were harvested and measured for auxin concentration distributions and metabolites to identify the common underlying mechanisms responsible for concentration difference of auxin.  Distribution of indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), and methylindole-3-acetic acid (Me-IAA) were determined and auxin concentration distributions were found to have a complex regulation mechanism.  The concentrations of IAA and Me-IAA in apical shoot were significantly different between elongation zone and mature zone resulting in an IAA gradient.  Tryptophan dependent pathway from tryptamine directly to IAA or through indole-3-acetonitrile to IAA and from indole-3-propionic acid (IPA) to IAA were three primary IAA synthesis pathways.  Moreover, some plant metabolites from flavonoid and phenylpropanoid synthesis pathways showed similar or reverse gradient and should involve in auxin homeostasis and concentration difference.  All the data give the first insight in the concentration difference and homeostasis of auxin in soybean seedlings and facilitate a deeper understanding of the molecular mechanism of stem development and growth.  The gathered information also helps to elucidate how plant height is formed in soybean and what strategy should be adopted to regulate the lodging resistance in soybean.

Received  21 December, 2017    Accepted  14 March, 2018

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The importance of microRNA (miRNA) at the post-transcriptional regulation level has recently been recognized in both animals and plants. In recent years, many studies focused on miRNA target identification and functional analysis. However, little is known about the transcription and regulation of miRNAs themselves. In this study, the transcription start sites (TSSs) for 11 miRNA primary transcripts of soybean from 11 miRNA loci (of 50 loci tested) were cloned by a 5´ rapid amplification of cDNA ends (5´ RACE) procedure using total RNA from 30-d-old seedlings. The features consistent with a RNA polymerase II mechanism of transcription were found among these miRNA loci. A position weight matrix algorithm was used to identify conserved motifs in miRNA core promoter regions. A canonical TATA box motif was identified upstream of the major start site at 8 (76%) of the mapped miRNA loci. Several cis-acting elements were predicted in the 2 kb 5´ to the TSSs. Potential spatial and temporal expression patterns of the miRNAs were found. The target genes for these miRNAs were also predicted and further elucidated for the potential function of the miRNAs. This research provides a molecular basis to explore regulatory mechanisms of miRNA expression, and a way to understand miRNAmediated regulatory pathways and networks in soybean.

To study the relationships between C4 enzyme activities and yield, C4 enzyme activities (phosphoenolpyruvate carboxylase (PEPCase), NADP-malate dehydrogenase (NADP-MDH), NADP-malic enzyme (NADP-ME), and pyruvate phosphate dikinase (PPDK)) in different organs of ten soybean cultivars with different yields were measured at different growth stages in China. The result showed that four enzyme activities in C4 pathway were obviously different among cultivars, especially PPDK activity was not detected in the leaves of Dongnong 1567 and Dongnong 1068 and the young leaves of Gongjiao 9107-1 and Dongnong 97-172, but there were weak activities in pod coats. The order of C4 enzyme activities is young leaves < old leaves < pod coats. The correlation coefficients between PEPCase activity and yield and between NADP-MDH activity at blooming stage and yield were 0.6979 and 0.6565, respectively, and both reached the significant level (5%), and PEPCase activity kept significant positive correlation with plant photosynthetic rate. There was a negative correlation between NADP-ME activity and yield, and no correlation was found between PPDK activity and yield.

EST-derived SSR marker has been developed in many species, but few methods of high efficiency have been reported for the exploitation of EST-SSR markers. Thus, a high efficiency method for mining millions of redundant EST data is needed. A modified method for the EST-SSR development with high efficiency was established based on the redundant EST data of soybean in this study. The method achieved its function through classifying ESTs according to the same SSR motif and detected candidate loci with redundant sequences. In this study, a total of 80 polymorphic EST-SSR markers of soybean were developed, 50 of them were exploited by this modified method which proved the higher speed and efficiency of this method. All the 80 polymorphic EST-SSRs were mapped on soybean physical map through in silico mapping and 15 markers were integrated on a genetic map constructed in previous study. A software named hpSSR (high polymorphic SSR) was programmed based on the concept of the up-built method for EST-SSR development. This method is not only pragmatic for EST-SSR exploitation in soybean, but also effective for the development of the marker in other species if the redundancy EST data is available.

Soyasaponins are valuable compounds in certain drugs, industry, food additives and surfactants. Selecting cultivars with higher-soyasaponin content along with agronomic traits is a main goal for many soybean breeders. The aim of the present study was to identify the quantitative trait loci (QTLs) associated with total soyasaponin content through a F2 population, which was derived from a cross between Ha 91016 (higher soyasaponin content cultivar, 16.8 mg g-1) and N98-9445A (lower soyasaponin content, only 5.7 mg g-1). A genetic linkage map including a total of 162 simple sequence repeat markers was constructed, which covered the total length 2 735.5 cM, and the average distance between markers was 16.96 cM. Two QTLs associated with total soyasaponin content were identified. One, qSAP_1 (located in sat_044-satt102 of linkage group (LG) K), could explain 12.6% of phenotypic variance. The other, qSAP_2, was located between satt368 and sat_413 of LG D1a, which could explain 15.8% of phenotypic variance. It was concluded that the two QTLs would have some potential value for marker-assisted selection for high-soyasaponin content breeding in soybeans.

The importance of microRNAs (miRNAs) at the post-transcriptional regulation level has recently been recognized in bothanimals and plants. In this study, the simple and most effective method of comparative genomic approach was used. Firstknown plants miRNAs BLAST against the soybean genome, and then the located candidates were searched for novelmiRNAs by RNA folding method in the vicinity (±400 nt) of the candidates. The results showed that a total of 521 novelsoybean miRNA genes, including 236 mature miRNAs, were identified. All these mature miRNAs were grouped into 58families, of which 21 of them were novel family in soybean. The upstream 2 000 nt of potential pre-miRNAs was used forpromoter prediction, in order to investigate prediction of miRNAs and detect transcript unit and clustering. In this study,miRNA genes less tend to be present as clusters in soybean. Only 9 clusters, containing 21 miRNA genes (accounted for4.0% of the total), were observed as part of polycistronic transcripts. Detailed analysis of sequence characteristics ofnovel miRNAs in soybean and all previous known plants miRNAs, were carried out. These results of this study providea reference point for further study on miRNAs identification in plants, and improve the understanding of genome insoybean.