Expression profiling of the BpIAA gene family and the determination of IAA levels in Betula platyphylla tetraploids

Betula platyphylla Sukaczev tetraploids have significantly larger leaf, fruit and stoma (gigantic phenotype) than diploids of the same species;however, the mechanism underlying this difference remains unclear. Tetraploid B. platyphylla transcriptome data have indicated that the expression of genes related to indole-3-acetic acid (IAA) biosynthesis and signal transduction was altered after genome duplication. IAA exerts pleiotropic effects on growth and development by inducing the expression of Aux/IAA. We identified 20 Aux/IAA genes (BpIAA1– BpIAA20) in B. platyphylla distributed across 10 chromosomes. Multiple alignment and motif analyses revealed that nine BpIAA proteins shared all four conserved domains. Phylogenetic analysis indicated that Aux/IAA families were divided into four subfamilies and that there were two pairs of BpIAA sister genes. The BpIAAs were differentially expressed in diploids and tetraploids. Moreover, the expression levels of the nine BpIAA genes were specifically up-regulated in tetraploids from June to September compared with May (except August 5th) in tetraploids, while they were down-regulated in diploids. IAA levels were more than twofold higher in tetraploids than diploids during the vegetative season. These results indicate that genome duplication of B. platyphylla caused the up-regulated of genes involved in IAA synthesis, and the increased concentration of IAA may induce the constitutive expression of 20 BpIAA genes. Therefore, the significant changes in the expression patterns of the BpIAAs contributed to the gigantic phenotype of tetraploids to some extent. Our research sheds light on the phenotypic variations observed in B. platyphylla tetraploids.

Cloning and Expression Analysis of THWRKY12 Gene from Tamarix hispida

[ Objective] This study aimed to clone and analyze the expression of THWRKY12 gene in Tamarix hispida. [Method] T. hispida seedlings were treated with 400 mmol/L NaC1 solutlon, 20% PEG and 100 μmol/L ABA, respectively. The expression of THIVRKY12 gene in different tissues was investigated by RT-PCR technology. [Result] Under treatments of NaC1 and PEG, the expression of THWRKY12 gene in different tissues of T. h/sp/da seedlings showed an overall upregulated trend, suggesting that THWRKYI2 is related with the saline-alkali resistance and drought resistance of T. hispida. Under ABA treatment, THWRKY12 gene had approximately the same expression pattern with the former two, indicating that THWRKY12 gene may involve in the regulation and control of the saline-al- kali resistance and drought resistance of T. hispida through the signal pathway regulated by ABA. [ Conclusion] This study laid foundation for investigating the functions of WRKY gene in the stress resistance of T. hispida.

Genetic overlap between salt and low-temperature tolerance loci at germination stage of soybean

Salt and low temperature were both very important factors for soybean production. It was necessary to improve the salt stress and low-temperature tolerance of soybean. The main purpose of this paper was to map the quantitative trait loci(QTL) related with salt tolerance and low- temperature tolerance at germination stage with backcross introgression lines(BILs),and analyze the genetic overlap between them. There were 22 QTL located with BC2 F4 introgression populations after salt stress,and 15 QTL were mapped after low-temperature stress. Seven overlapping QTLs between salt tolerance and low-temperature tolerance were detected on 6 linkage groups at germination stage. In total,there were 31.81 % of salt tolerance and low-temperature tolerance loci existed genetic overlap.

Early evaluation of growth traits of Larix kaempferi clones

Early selection is an important method to shorten the breeding cycle for tree species, which may differ in the time for early selection. To evaluate the early selected time for Larix kaempferi, tree height and diameter at breast height of 57 L. kaempferi clones were measured over many different growth years. The results indicated that, except for age × clone interaction for diameter at breast height （P = 0.741）, there were significant differences among all variation sources （P 〈 0.01）. The coefficient of phenotypic variation ranged from 14.89 to 35.65% for height and from 19.17 to 23.86% for diameter at breast height in different growth years. The repeatability of height and of diameter at breast height among clones was high, ranging from 0.6181 to 0.8531 （height） and from 0.8443 to 0.8497 （diameter at breast height）, in different growth years. There were significant positive correlations between all pairs of growth traits except between height in the 2nd growth year and height in the 30th growth year; and between height in the 2nd growth year × diameter at breast height in the 30th growth year. With a comprehen- sive evaluation method and a selection ratio of 10%, L65, L1, L62, L9, L15, and L78 were selected as excellent clones in the 30th growth year. Their average values of height and diameter at breast height were 9.81 and 16.57% higher than the overall average, representing genetic gains of 6.46 and 13.99%, respectively. This study provides a theoretical foundation for the genetic improvement of L. kaempferi.