Sugar content is a determinant of apple (Malus×domestica Borkh.) sweetness.  However, the molecular mechanism underlying sucrose accumulation in apple fruit remains elusive.  Herein, this study reported the role of the sucrose transporter MdSUT2.1 in the regulation of sucrose accumulation in apples.  The MdSUT2.1 gene encoded a protein with 612 amino acid residues that could be localized at the plasma membrane when expressed in tobacco leaf protoplasts.  MdSUT2.1 was highly expressed in fruit and was positively correlated with sucrose accumulation during apple fruit development.  Moreover, complementary growth assays in a yeast mutant validated the sucrose transport activity of MdSUT2.1.  MdSUT2.1 overexpression in apples and tomatoes resulted in significant increases in sucrose, fructose, and glucose contents compared to the wild type (WT).  Further analysis revealed that the expression levels of sugar metabolism- and transport-related genes SUSYs, NINVs, FRKs, HXKs, and TSTs increased in apples and tomatoes with MdSUT2.1 overexpression compared to WT.  Finally, unlike the tonoplast sugar transporters MdTST1 and MdTST2, the promoter of MdSUT2.1 was not induced by exogenous sugars.  These findings provide valuable insights into the molecular mechanism underlying sugar accumulation in apples.

 

Starch is the most important component in endosperm of sorghum grain.  Usually, two types of starch are present: amylose (AM) and amylopectin (AP).  The levels of AM and AP contents play a significant role in the appearance, structure, and quality of sorghum grains and in marketing applications.  In the present study, a panel of 634 sorghum (Sorghum bicolor (L.) Moench) accessions were evaluated for starch, AM, and AP contents of grain, which included a mini core collection of 242 accessions from the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) in India, and 252 landraces and 140 cultivars from China.  The average starch content was 67.64% and the average AM and AP contents were 20.19 and 79.81%, respectively.  We developed a total of 260 000 high-confidence single nucleotide polymorphism (SNP) markers in the panel of 634 accessions of S. bicolor using specific locus amplified fragment sequencing (SLAF-seq).  We performed genome-wide association studies (GWAS) of starch, AM, and AM/AP of grain and SNP markers based on a mixed linear model (MLM).  In total, 70 significant association signals were detected for starch, AM, and AM/AP ratio of grain with P<4.452×10^–7, of which 10 SNPs were identified with significant starch, 51 SNPs were associated with AM, and nine SNPs were associated with the AM/AP ratio.  The Gene Ontology (GO) analysis identified 12 candidate genes at five QTLs associated with starch metabolism within the 200-kb intervals, located on chromosomes 1, 5, 6, and 9.  Of these genes, Sobic.006G036500.1 encodes peptidyl-prolyl cis-trans-isomerase CYP38 responsible for hexose monophosphate shunt (HMS) and Sobic.009G071800 encodes 6-phospho-fructokinase (PFK), which is involved in the embden-meyerhof pathway (EMP).  Kompetitive allele specific PCR (KASP) markers were developed to validate the GWAS results.  The C allele is correlated with a high starch content, while the T allele is linked with a low level of starch content, and provides reliable haplotypes for MAS in sorghum quality improvement.

Sucrose is known to play an important role in the cryopreservation of sperm and female gonads; however, its effect on the cryopreservation of pig spermatogonial stem cells (pSSCs) has not been tested.  The aim of this work was to study the effect of sucrose during pSSC cryopreservation and to find the most effective concentration in freezing medium.  pSSCs were cryopreserved with freezing media containing different concentrations of sucrose (70, 140, 210, and 280 mmol L^–1) and a control group without sucrose.  The survival rates, plasma membrane integrity, and mitochondrial membrane potential of thawed cells were detected by trypan blue (TB) staining, SYBR-14/propidium iodide (PI) dual staining, and JC-1 staining, respectively.  All the staining results showed an obvious increase in cell survival in the sucrose-treated groups as compared to that in the control group, with the exception of 280 mmol L^–1 sucrose.  Moreover, the 210 mmol L^–1 sucrose group yielded the highest survival rate among all the groups (P<0.05).  The results of SYBR-14/PI dual staining and JC-1 staining were consistent with those of TB staining as above described.  Quantitative real-time PCR (qRT-PCR) indicated that the mRNA levels of three apoptosis-promoting genes (BAX, APAF1 and CASPASE9) were significantly higher in thawed cells than in cells before freezing (P<0.05).  Moreover, the mRNA level of one anti-apoptotic gene (XIAP) was significantly lower in thawed cells than in cells before freezing (P<0.05).  When comparing the mRNA expression of apoptosis-related genes in thawed cells, the mRNA level of the anti-apoptotic genes in the control group was significantly lower than that in the sucrose-treated
groups (P<0.05).  Western blot analyses showed that the expression levels of cleaved CASPASE9, CASPASE3 and PARP-1 in the sucrose-treated groups were lower than those in the control group and were the lowest in the 210 mmol L^–1 sucrose group.  Both qRT-PCR and Western blot analyses suggested that sucrose inhibited cell apoptosis during freezing and thawing.  Briefly, sucrose promoted pSSCs survival after freezing and thawing, especially at a concentration of 210 mmol L^–1, which possibly assisted pSSC dehydration and inhibited cell apoptosis.  These findings hold great promise for further studies of the regulatory mechanism of proliferation and differentiation of pSSCs. 

In this study we report the results of a decade-long breeding program for japonica super rice made by Nanjing Branch of Chinese National Center for Rice Improvement in Jiangsu Academy of Agricultural Sciences.  We concluded that selection of parents with good comprehensive traits and complementary advantages and disadvantages of both parents in the hybrid combination, and early selection of high heritability traits in earlier segregating generations could significantly improve the breeding efficiency.  The use of closely-linked functional markers in pyramiding of multiple genes could greatly increase breeding efficiency, avoiding time-consuming and laborious steps that were used in traditional breeding program.  It is also important to coordinate the yield components with variety characteristics such as yield stability, wide adaptability, lodging resistance, and an attractive grain appearance during late growth stage of rice.