The role of γ-aminobutyric acid in aluminum stress tolerance in a woody plant, Liriodendron chinense×tulipifera

The aluminum(Al)cation Al^(3+)in acidic soil shows severe rhizotoxicity that inhibits plant growth and development.Most woody plants adapted to acidic soils have evolved specific strategies against Al^(3+)toxicity,but the underlying mechanism remains elusive.The four-carbon amino acid gamma-aminobutyric acid(GABA)has been well studied in mammals as an inhibitory neurotransmitter;GABA also controls many physiological responses during environmental or biotic stress.The woody plant hybrid Liriodendron(L.chinense×tulipifera)is widely cultivated in China as a horticultural tree and provides high-quality timber;studying its adaptation to high Al stress is important for harnessing its ecological and economic potential.Here,we performed quantitative iTRAQ(isobaric tags for relative and absolute quantification)to study how protein expression is altered in hybrid Liriodendron leaves subjected to Al stress.Hybrid Liriodendron shows differential accumulation of several proteins related to cell wall biosynthesis,sugar and proline metabolism,antioxidant activity,cell autophagy,protein ubiquitination degradation,and anion transport in response to Al damage.We observed that Al stress upregulated glutamate decarboxylase(GAD)and its activity,leading to increased GABA biosynthesis.Additional GABA synergistically increased Al-induced antioxidant enzyme activity to efficiently scavenge ROS,enhanced proline biosynthesis,and upregulated the expression of MATE1/2,which subsequently promoted the efflux of citrate for chelation of Al^(3+).We also showed similar effects of GABA on enhanced Al^(3+)tolerance in Arabidopsis.Thus,our findings suggest a function of GABA signaling in enhancing hybrid Liriodendron tolerance to Al stress through promoting organic acid transport and sustaining the cellular redox and osmotic balance.

The Regulatory Roles of microRNAs and Associated Target Genes during Early Somatic Embryogenesis in Liriodendron Sino-Americanum

Somatic cells respond to considerable stress,and go through a series of phytohormone pathways,then forming an embryo.The developmental process is recorded as somatic embryogenesis(SE).One of the key components regulating SE are the microRNAs(miRNAs).Despite previous studies,it is still not clear exactly how miRNAs exert their function of regulating targets during conditionally activated early SE.Here,we use Liriodendron sino-americanum as a model system and perform a combined analysis of microfluidic chips and degradome sequencing to study this process.We identified a total of 386 conserved miRNAs and 153 novel miRNAs during early SE.According to the ANOVA test,239 miRNAs showed 12 distinct expression patterns.Through degradome sequencing,419 targets and 198 targets were identified for 136 known miRNAs and 37 novel miRNAs,respectively.Gene Ontology(GO)and metabolism pathway enrichment analysis revealed that these targets were significantly involved in oxidation-reduction processes,calmodulin-mediated signal transduction pathways and carbohydrate metabolism.The genes that were related to stress responses,phytohormone pathways and plant metabolism were identified within the targets of miR319,miR395,miR408,miR472,miR482,miR390,miR2055,miR156,miR157,miR171,miR396,miR397,miR529,miR535 and miR159.According to promoter analysis,various cis-acting elements related to plant growth and development,phytohormones response and stress response were present in the promoter of the miRNAs.The differential expression patterns of 11 miRNA-target modules were confirmed by real-time quantitative PCR.The study demonstrated that the miRNA plays an important role in the early SE process by regulating its target and then participating in carbohydrate metabolism and stress response.It also provided a valuable resource for further research in determining the genetic mechanism of SE,and then facilitating breeding programs on plants.

Efficient Evergreen Plant Regeneration of Cinnamomum japonicum Sieb.through in vitro Organogenesis

Cinnamomum japonicum Sieb.is an excellent roadside tree and medicinal tree species with considerable ornamental and economic value.In this study,we successfully developed a large-scale micropropagation protocol for C.japonicum for the first time.Sterilized shoots were excised and used as explants for shoot induction on several basal media,supplemented with different concentrations of plant growth regulators(PGRs),such as Thidiazuron(TDZ),N^(6)-Benzyladenine(6-benzylaminopurine)(BA),α-naphthaleneacetic acid(NAA)and Gibberellic acid(GA_(3)).After comparison,the most efficient medium for shoot regeneration was 1/2 Murashige and Skoog(MS)medium containing 0.5 mg L^(-1)BA,0.05 mg L^(-1)NAA and 0.2 mg L^(-1)GA_(3),which resulted in an average number of induced shoots per explant and shoot length of 5.2 and 1.62 cm at 28 d,respectively.Then,elongated adventitious shoots were transferred to induce roots.86.7%of shoots was able to root on 1/2 MS medium supplemented with 0.5 mg L^(-1)NAA and 0.1 mg L^(-1)BA.The earliest rooting time observed was after 21 d and the average root length was up to 3.3 cm after 28 d.Our study shows that C.japonicum can be successfully regenerated through de novo organogenesis,which lays a foundation for future transformation research on this tree.