Overexpression of Larch SCL6 Inhibits Transitions from Vegetative Meristem to Inflorescence and Flower Meristem in Arabidopsis thaliana (L.) Heynh.

SCARECROW-LIKE6 (SCL6) plays a role in the formation and maintenance of the meristem. In Larix kaempferi (Lamb.) Carr., an important afforestation tree species in China, SCL6 (LaSCL6) has two alternative splicing variants-LaSCL6-var1 and LaSCL6-var2-which are regulated by microRNA171. However, their roles are still unclear. In this study, LaSCL6-var1 and LaSCL6-var2 were transformed into the Arabidopsis thaliana (L.) Heynh. genome, and the phenotypic characteristics of transgenic A. thaliana, including the germination percentage, root length, bolting time, flower and silique formation times, inflorescence axis length, and branch and silique numbers, were analyzed to reveal their functions. It was found that LaSCL6-var1 and LaSCL6-var2 overexpression shortened the root length by 41% and 31%, respectively, and increased the inflorescence axis length. Compared with the wild type, the bolting time in transgenic plants was delayed by approximately 2-3 days, the first flower and silique formation times were delayed by approximately 3-4 days, and the last flower and silique formation times were delayed by about 5 days. Overall, the life cycle in transgenic plants was prolonged by approximately 5 days. These results show that LaSCL6 overexpression inhibited the transitions from the vegetative meristem to inflorescence meristem and from the flower meristem to meristem arrest in A. thaliana, revealing the roles of LaSCL6-var1 and LaSCL6-var2 in the fate transition and maintenance of the meristem.

LaDAL1 Coordinates Age and Environmental Signals in the Life Cycle of Larix kaempferi.

Perennial woody plants are long-lived, and their life-cycle events occur in order in each generation, but what drives the occurrence and restart of these events in their offspring is unknown. Based on its age-dependent expression pattern and function, Larix kaempferi DEFICIENS-AGAMOUS-LIKE 1 (LaDAL1), a MADS transcription factor has been suggested to be a time recorder and life-cycle event coordinator. Here, we studied the dynamic spatiotemporal expression pattern of LaDAL1 in the life cycle of L. kaempferi to analyze the molecular mechanism of life-cycle progression. In full view of the life cycle, LaDAL1 transcription was related with life-cycle progression, and its transcript level increased sharply from age 3 to 5 years, which might be the molecular characteristic of the vegetative phase change, and then stayed at a high level. During sexual reproduction, LaDAL1 transcript level decreased sequentially during meiosis and embryogenesis, suggesting that meiosis rapidly lowers the age signal, and after fertilization, the age signal was reset to "0" with the embryogenesis. When a seed germinates, the next generation restarts, and the age is re-counted. Altogether, these results not only provide important and novel insights into the life-cycle progression and transgeneration in perennial woody plants, but also advance our understanding of age recording.

Concerted control of the LaRAV1-LaCDKB1;3 module by temperature during dormancy release and reactivation of larch.

Dormancy release and reactivation of temperate-zone trees involve the temperature-modulated expression of cell-cycle genes. However, information on the detailed regulatory mechanism is limited. Here, we compared the transcriptomes of the stems of active and dormant larch trees, emphasizing the expression patterns of cell-cycle genes and transcription factors and assessed their relationships and responses to temperatures. Twelve cell-cycle genes and 31 transcription factors were strongly expressed in the active stage. Promoter analysis suggested that these 12 genes might be regulated by transcription factors from 10 families. Altogether, 73 cases of regulation between 16 transcription factors and 12 cell-cycle genes were predicted, while the regulatory interactions between LaMYB20 and LaCYCB1;1, and LaRAV1 and LaCDKB1;3 were confirmed by yeast one-hybrid and dual-luciferase assays. Last, we found that LaRAV1 and LaCDKB1;3 had almost the same expression patterns during dormancy release and reactivation induced naturally or artificially by temperature, indicating that the LaRAV1-LaCDKB1;3 module functions in the temperature-modulated dormancy release and reactivation of larch trees. These results provide new insights into the link between temperature and cell-cycle gene expression, helping to understand the temperature control of tree growth and development in the context of climate change.

Comparative transcriptomic analysis of the flower induction and development of the Lei bamboo (Phyllostachys violascens).

BACKGROUND: Bamboo is a very important forest resource. However, the prolonged vegetative stages and uncertainty of flowering brings difficulties in bamboo flowers sampling. Until now, the flowering mechanism of bamboo is still unclear. RESULTS: In this study, three successive stages of flowering buds and the corresponding vegetative buds (non-flowering stage) from Lei bamboo (Phyllostachys violascens) were collected for transcriptome analysis using Illumina RNA-Seq method. We generated about 442 million clean reads from the above samples, and 132,678 unigenes were acquired with N50 of 1080 bp. A total of 7266 differentially expressed genes (DEGs) were determined. According to expression profile and gene function analysis, some environmental stress responsive and plant hormone-related DEGs were highly expressed in the inflorescence meristem formation stage (TF_1) while some floral organ development related genes were up-regulated significantly in floral organs determination stage (TF_2) and floral organs maturation (TF_3) stage, implying the essential roles of these DEGs in flower induction and maturation of Lei bamboo. Additionally, a total of 25 MADS-box unigenes were identified. Based on the expression profile, B, C/D and E clade genes were more related to floral organs development compared with A clade genes in Lei bamboo. CONCLUSIONS: This transcriptome data presents fundamental information about the genes and pathways involved in flower induction and development of Lei bamboo. Moreover, a critical sampling method is provided which could be benefit for bamboo flowering mechanism study.

Callus induction and regeneration via shoot tips of Dendrocalamus hamiltonii.

By using shoot tips as explants, various media and culture conditions for callus induction and proliferation, shoot differentiation, root induction and plantlet transplantation to develop an efficient and reliable regeneration system with Dendrocalamus hamiltonii were tested. Murashige and Skoog (MS) medium supplemented with 3 mg/l 2, 4-dichlorophenoxyacetic acid, 1 mg/l benzyladenine (BA), 500 mg/l glutamine, 500 mg/l proline, and 500 mg/l casein hydrolysate yielded the best rates of callus induction and granular-compact callus induction. MS medium supplemented with 1 mg/l BA, 0.3 mg/l kinetin and 0.3 mg/l naphthaleneacetic acid conferred the highest differentiation rate of calli. The maximum rooting rate was obtained in 1/2 MS medium supplemented with 3 mg/l indole-3-butyric acid, and the roots were long and thick. All hardened plantlets survived after transfer to an equal ratio mixture of peat, vermiculite and perlite. The regeneration system of D. hamiltonii developed is efficient and provides a useful tool for genetic transformation in bamboo species.

Functional analysis of PI-like gene in relation to flower development from bamboo (Bambusa oldhamii).

Bamboo flowering owns many unique characteristics and remains a mystery. To investigate the molecular mechanisms underlying flower development in bamboo, a petal-identity gene was identified as a PISTILLATA homologue named BoPI from Bambusa oldhamii (bamboo family). Expression analysis showed that BoPI was highly expressed in flower organs and gradually increased during flower development stage, suggesting that BoPI played an important role in flower development. Ectopic expression of BoPI in Arabidopsis caused conversion of sepals to petals. 35S::BoPI fully rescued the defective petal formation in the pi-1 mutant. BoPI could interact with BoAP3 protein in vitro. These results suggested that BoPI regulated flower development of bamboo in a similar way with PI. Besides flower organs, BoPI was also expressed in leaf and branch, which revealed that BoPI may involve in leaf and branch development. Similar to other MIKC-type gene, BoPI contained the Cterminal sequence but its function was controversial. Ectopic expression of the C-terminal deletion construct (BoPI- ∆C) in Arabidopsis converted sepals to petals; BoPI- ∆C interacted with BoAP3 on yeast two-hybrid assay, just like the full-length con struct. The result implied that the C-terminal sequence may not be absolutely required for organ identity function in the context of BoPI.