Genome-wide identification and expression analysis of phenylalanine ammonia-lyase (PAL) family in rapeseed (Brassica napus L.)

BACKGROUND

Phenylalanine ammonia-lyase (PAL), as a key enzyme in the phenylalanine metabolism pathway in plants, plays an important role in the response to environmental stress. However, the PAL family responding to abiotic stress has not been fully characterized in rapeseed.

RESULTS

In this study, we conducted a genome-wide study of PAL family, and analyzed their gene structure, gene duplication, conserved motifs, cis-acting elements and response to stress treatment. A total of 17 PALs were identified in the rapeseed genome. Based on phylogenetic analysis, the BnPALs were divided into four clades (I, II, IV, and V). The prediction of protein structure domain presented that all BnPAL members contained a conservative PAL domain. Promoter sequence analysis showed that the BnPALs contain many cis-acting elements related to hormone and stress responses, indicating that BnPALs are widely involved in various biological regulatory processes. The expression profile showed that the BnPALs were significantly induced under different stress treatments (NaCl, Na2CO3, AlCl3, and PEG), suggesting that BnPAL family played an important role in response to abiotic stress.

CONCLUSIONS

Taken together, our research results comprehensively characterized the BnPAL family, and provided a valuable reference for revealing the role of BnPALs in the regulation of abiotic stress responses in rapeseed.

Physiological and molecular mechanism of cadmium (Cd) tolerance at initial growth stage in rapeseed (Brassica napus L.)

Cadmium (Cd) contaminated soil has threatened plant growth and human health. Rapeseed (Brassica napus L.), an ideal plant for phytoremediation, is an important source of edible vegetable oil, vegetable, animal fodder, green manure and biodiesel. For safe utilization of Cd polluted soil, physiological, biochemical, and molecular techniques have been used to understand mechanisms of Cd tolerance in B. napus. However, most of these researches have concentrated on vegetative and adult stages, just a few reports focus on the initial growth stage. Here, the partitioning of cadmium, gene expression level and activity of enzymatic antioxidants of H18 (tolerant genotype) and P9 (sensitive genotype) were investigated under 0 and 30 mg/L Cd stress at seedling establishment stage. Results shown that the radicle length of H18 and P9 under Cd stress were decreased by 30.33 (0.01 < P < 0.05) and 88.89% (P < 0.01) respectively. Cd concentration at cotyledon not radicle and hypocotyl in P9 was significantly higher than that in H18. The expression level of BnaHMA4c, which plays a key role in root-to-shoot translocation of Cd, was extremely higher in P9 than in H18 under both normal and Cd stress conditions. We also found that SOD, CAT and POD were more active in responding to Cd stress after 48 h, and the activity of SOD and CAT in H18 were higher than that in P9 at all observed time points. In conclusion, high activity of enzymatic antioxidants at initial Cd stress stage is the main detoxification mechanism in Cd-tolerant rapeseed, while the higher Cd transfer coefficient, driven by higher expression level of BnaHMA4c is the main mechanism for surviving radicle from initial Cd toxicity in Cd-sensitive rapeseed.

Optimal Nitrogen Fertilization Management of Seed-sowing Rapeseed in Yangtze River Basin of China

BACKGROUND AND OBJECTIVE

For cultivation and high yield of oilseed rape (Brassica napus L.) in China, traditional seedling transplanting is replaced by seed-sowing but, better nitrogen management is crucial and not established yet. This study aimed to adapt N management to the seed-sowing method for the winter oilseed rape and to minimize the N fertilizer-derived pollution potential in the upper reaches of Yangtze River Basin.

MATERIALS AND METHODS

Three field experiments were conducted to check effect of different doses of N fertilizers, split doses of N and different types of N fertilizers for seed-sowing winter oilseed rape with high plant density in upper reaches of Yangtze River Basin in Sichuan province of China.

RESULTS

In first experiment, among four doses (0, 90, 180 and 270 kg N ha-1) on average 3.54 t ha-1 was in 180 kg N ha-1 and 3.61 t ha-1 in 270 kg N ha-1 while cultivars dy6 and cn3 produced 3.23 and 3.29 t ha-1 which is significantly higher than zs11. There was no significant difference in N-use efficiency among three cultivars tested and second experiment showed no significant difference in seed yield with split N application. The third experiment compared the effects of different fertilizer types (urea, coated urea, 1:1 mixture of urea and coated urea and compound nitrogen fertilizer) on seed yield and get no significant difference in seed yield.

CONCLUSION

This experiment proved that seed sowing method with higher nitrogen had high yield in the upper reaches of Yangtze River Basin in China, but higher N application may cause environment pollution. So, seed sowing method with nitrogen 180 kg N ha-1 was proved to be more effective.

Genetic dissection of the mechanism of flowering time based on an environmentally stable and specific QTL in Brassica napus

Flowering time is an important agronomic trait that is highly influenced by the environment. To elucidate the genetic mechanism of flowering time in rapeseed (Brassica napus L.), a genome-wide QTL analysis was performed in a doubled haploid population grown in winter, semi-winter and spring ecological conditions. Fifty-five consensus QTLs were identified after combining phenotype and genomic data, including 12 environment-stable QTLs and 43 environment-specific QTLs. Importantly, six major QTLs for flowering time were identified, of which two were considered environment-specific QTLs in spring ecological condition and four were considered environment-stable QTLs in winter and semi-winter ecological conditions. Through QTL comparison, 18 QTLs were colocalized with QTLs from six other published studies. Combining the candidate genes with their functional annotation, in 49 of 55 consensus QTLs, 151 candidate genes in B. napus corresponding to 95 homologous genes in Arabidopsis thaliana related to flowering were identified, including BnaC03g32910D (CO), BnaA02g12130D (FT) and BnaA03g13630D (FLC). Most of the candidate genes were involved in different flowering regulatory pathways. Based on re-sequencing and differences in sequence annotation between the two parents, we found that regions containing some candidate genes have numerous non-frameshift InDels and many non- synonymous mutations, which might directly lead to gene functional variation. Flowering time was negativly correlated with seed yield and thousand seed weight based on a QTL comparison of flowering time and seed yield traits, which has implications in breeding new early-maturing varieties of B. napus. Moreover, a putative flowering regulatory network was constructed, including the photoperiod, circadian clock, vernalization, autonomous and gibberellin pathways. Multiple copies of genes led to functional difference among the different copies of homologous genes, which also increased the complexity of the flowering regulatory networks. Taken together, the present results not only provide new insights into the genetic regulatory network underlying the control of flowering time but also improve our understanding of flowering time regulatory pathways in rapeseed.