Transcriptome and metabolome analyses reveal novel insights into the seed germination of Michelia chapensis, an endangered species in China

Elucidating the regulatory role of long non-coding RNAs in drought stress response during seed germination in leaf mustard

Leaf mustard (Brassica juncea L. Czern & Coss), an important vegetable crop, experiences pronounced adversity due to seasonal drought stress, particularly at the seed germination stage. Although there is partial comprehension of drought-responsive genes, the role of long non-coding RNAs (lncRNAs) in adjusting mustard's drought stress response is largely unexplored. In this study, we showed that the drought-tolerant cultivar 'Weiliang' manifested a markedly lower base water potential (-1.073 MPa vs -0.437 MPa) and higher germination percentage (41.2% vs 0%) than the drought-susceptible cultivar 'Shuidong' under drought conditions. High throughput RNA sequencing techniques revealed a significant repertoire of lncRNAs from both cultivars during germination under drought stress, resulting in the identification of 2,087 differentially expressed lncRNAs (DELs) and their correspondingly linked 12,433 target genes. It was noted that 84 genes targeted by DEL exhibited enrichment in the photosynthesis pathway. Gene network construction showed that MSTRG.150397, a regulatory lncRNA, was inferred to potentially modulate key photosynthetic genes (Psb27, PetC, PetH, and PsbW), whilst MSTRG.107159 was indicated as an inhibitory regulator of six drought-responsive PIP genes. Further, weighted gene co-expression network analysis (WGCNA) corroborated the involvement of light intensity and stress response genes targeted by the identified DELs. The precision and regulatory impact of lncRNA were verified through qPCR. This study extends our knowledge of the regulatory mechanisms governing drought stress responses in mustard, which will help strategies to augment drought tolerance in this crop.

Methodological and Physiological Study during Seed Dormancy Release of Symplocos paniculata

Symplocos paniculata are reported to exhibit seed dormancy, which impedes its cultivation and widespread adoption. In this study, a comprehensive method was established to overcome seed dormancy by subjecting seeds to scarification in 98% H2SO4 for 10 min, followed by 1000 mg·L-1 GA3 soaking for 48 h and stratification at 4 °C for 100 days. The seed germination percentage has increased significantly, to a peak of 42.67%, though the seeds could not germinate timely by NaOH scarification. Additionally, the dynamic changes of key stored substances (proteins, soluble sugars, starches, and fats), associated enzyme activities (amylases, peroxidase, and catalase), and endogenous hormones (abscisic acid, gibberellic acid, and indole-3-acetic acid) in seeds were investigated. The results demonstrated a continuous degradation of starch and fat in S. paniculata seeds, while the levels of protein and soluble sugar exhibited fluctuations, which probably facilitated seed dormancy breaking through energy supply and transformation. The enzymatic activities underwent rapid changes, accompanied by a gradual decrease in ABA content within the seeds with increasing stratification time. Notably, GA3, GA3/ABA, and (GA3 + IAA)/ABA showed significant increases, indicating their positive regulatory roles in seed germination. This study clarified the dormancy mechanism and established an effective method for the release dormancy of S. paniculata seeds.

Characterization and mechanism of seed dormancy in Symplocos paniculata

Symplocos paniculata is a highly desirable oil species for biodiesel and premium edible oil feedstock. While germplasm preservation and breeding are crucial, the severity of seed dormancy poses a challenge to successful germination. We employed S. paniculata seeds as experimental materials and conducted an investigation into the types and causes of seed dormancy by analyzing the morphology and developmental characteristics of its embryo, exploring the water permeability property of the endocarp, and examining the presence of endogenous inhibitors, aiming to establish a theoretical foundation for overcoming seed dormancy and maximizing germplasm resource utilization. The findings revealed that the seed embryo had matured into a fully developed embryo, and no dormancy in terms of embryo morphology was observed. Upon reaching maturity, the endocarp of seeds undergoes significant lignification, resulting in notable differences in water absorption between cracked and intact seeds. The impermeability of the endocarp is one of the factors contributing to mechanical restriction. The different phases of endosperm extraction exerted varying effects on the germination of Chinese cabbage seeds, with the methanol phase exhibiting the most potent inhibitory effect. The presence of endogenous inhibitors emerged as the primary factor contributing to physiological dormancy in seeds. GC-MS analysis and validation trials revealed that fatty acids and phenolics, including hexadecanoic acid, oxadecanoic acid, and m-cresol, constituted the main types of endogenous inhibitory compounds found within the endosperm. These findings suggest that the seed dormancy in S. paniculata seeds has endocarp mechanical restriction, and the presence of endogenous inhibitors causes physiological dormancy.