Overexpression of the LcPIN2 and LtPIN2 Gene in Arabidopsis thaliana Promotes Root Elongation

The auxin polar transporter,PIN-FORMED 2(PIN2)plays an important role in root development.However,it remains unclear whether PIN2 genes form two Liriodendron species,L.chinense(LcPIN2)and L.tulipifera(LtPIN2),are both involved in root development and whether and to what extent these two genes diverge in function.Here,we cloned and overexpressed LcPIN2 and LtPIN2 in Arabidopsis thaliana wild-type(WT)and Atpin2 mutant.Phylogenetic and sequence analysis showed a small degree of differentiation between these two Liriodendron PIN2 genes.Tissue-specific gene expression analysis indicated that both Liriodendron PIN2 genes were highly expressed in roots,implying a potential role in root development.Finally,heterologous overexpression of LcPIN2 and LtPIN2 in Arabidopsis both significantly increased the root length compared to wild-type and empty vector.Furthermore,the root length defect in Atpin2 was complemented both by LcPIN2 and LtPIN2.However,heterologous overexpression of LcPIN2 and LtPIN2 cannot rescue the defect in root gravitropism of Atpin2 mutants.Taken together,ourfindings unravel PIN2 genes from the magnoliids plant Liriodendron were functionally conserved with AtPIN2 in the dicotyledonous plant Arabidopsis in regard to the regulation of root length,but not root gravitropism.This study also provides a potential target for genetic improvement of the root system in these valuable forest trees Liriodendron.

Transcriptome analysis and metabolic profiling reveal the key role of carotenoids in the petal coloration of Liriodendron tulipifera

Liriodendron tulipifera,also known as tuliptree,is a popular ornamental horticultural plant with extraordinary tulipshaped flowers characterized by an orange band near their base.The mechanisms underlying petal band-specific pigmentation during L.tulipifera flower development are unclear.Here,we combined nontargeted and targeted metabolomics and transcriptomics to identify a pathway cascade leading to carotenoid biosynthesis that is specifically activated in the petal band.The comparative analysis of carotenoid metabolites between L.tulipifera and Liriodendron hybrids indicates thatγ-carotene,a rare carotene in plants,is the most likely orange pigment responsible for the coloration of the petal band.Phenotypic and transcriptomic analyses of developing petals reveal that the band area is first predefined by the loss of green color.Later,the band is maintained by locally activating and repressing carotenoid and chlorophyll biosynthesis genes,respectively.Two rate-limiting genes of carotene biosynthesis,carotenoid isomerase(CRTISO)and epsilon lycopene cyclase(ε-LCY),encode the core enzymes responsible for petal band-specific orange pigmentation in L.tulipifera.In particular,a putative additionalε-LCY copy specific to L.tulipifera may contribute to the distinct petal coloration pattern,compared with L.chinense.Taken together,our work provides a first glimpse of the metabolome and transcriptome dynamics in tuliptree flower coloration and provides a valuable resource for flower breeding or metabolic engineering as well as for understanding flower evolution in an early woody angiosperm.

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.

Morphological, phenological, and transcriptional analyses provide in sight into the diverse flowering traits of a mutant of the relic woody plant Liriodendron chinense

Flowering is crucial to plant reproduction and controlled by multiple factors.However,the mechanisms underlying the regulation of flowering in perennial plants are still largely unknown.Here,we first report a super long blooming 1(slbl)mutant of the relict tree Liriodendron chinense possessing a prolonged blooming period of more than 5 months,in contrast to the 1 month blooming period in the wild type(WT).Phenotypic characterization showed that earlier maturation of lateral shoots was caused by accelerated axillary bud fate,leading to the phenotype of continuous flowering in slbl mutants.The transcriptional activity of genes related to hormone signaling(auxin,cytokinin,and strigolactone),nutrient availability,and oxidative stress relief further indicated active outgrowth of lateral buds in slbl mutants.Interestingly,we discovered a unique FT splicing variant with intron retention specific to slbl mutants,representing a potential causal mutation in the slbl mutants.Surprisingly,most slbl inbred offspring flowered precociously with shorter juvenility(~4 months)than that(usually 8-10 years)required in WT plants,indicating heritable variation underlying continuous flowering in slbl mutants.This study reports an example of a perennial tree mutant that flowers continuously,providing a rare resource for both breeding and genetic research.