Abstract
Maintaining the viability of the apical shoot is critical for continued vertical growth in plants. Terminal shoot of tree species Paulownia cannot regrow in subsequent years. The short day (SD) treatment leads to apical growth cessation and dormancy. To understand the molecular basis of this, we further conducted global RNA-Seq based transcriptomic analysis in apical shoots to check regulation of gene expression. We obtained ~219 million paired-end 125-bp Illumina reads from five time-courses and de novo assembled them to yield 49,054 unigenes. Compared with the untreated control, we identified 1540 differentially expressed genes (DEGs) which were found to involve in 116 metabolic pathways. Expression of 87% of DEGs exhibited switch-on or switch-off pattern, indicating key roles in growth cessation. Most DEGs were enriched in the biological process of gene ontology categories and at later treatment stages. The pathways of auxin and circadian network were most affected and the expression of associated DEGs was characterised. During SD induction, auxin genes IAA, ARF and SAURs were down-regulated and circadian genes including PIF3 and PRR5 were up-regulated. PEPC in photosynthesis was constitutively upregulated, suggesting a still high CO2 concentrating activity; however, the converting CO2 to G3P in the Calvin cycle is low, supported by reduced expression of GAPDH encoding the catalysing enzyme for this step. This indicates a de-coupling point in the carbon fixation. The results help elucidate the molecular mechanisms for SD inducing dormancy and cessation in apical shoots.
Highlights
Plant dormancy is a temporary, visible suspension in meristem, which is an adaptation for survival and growth in response to environmental stresses, especially for temperate plants
We treated one-year-old young trees propagated from roots of Paulownia cultivar P. tomentosa with short-day cycles of 8 h light and 16 h darkness in a greenhouse during the fastest growing season in August. 0.5 cm shoot tips from eight trees were sampled on Aug 1st (S1) as a control before the short day (SD) treatment, and similar tissues were collected at five-day intervals on Aug 6 (S2), 11 (S3), 16 (S4) and 21 (S5)
Obvious growth cessation and dormancy induction in shoot tips were observed after SD treatment (Fig. 1a–e), whereas the shoot tips under a long-day photoperiod were still in a fast-growing condition, the same as at S1
Summary
Plant dormancy is a temporary, visible suspension in meristem, which is an adaptation for survival and growth in response to environmental stresses, especially for temperate plants. The short day (SD) photoperiod is known to play a crucial role in plant growth cessation, dormancy induction and dormant bud formation[1]. Down-regulated FT expression under SD leads to growth cessation and dormancy in Populus. Over-expression of the basic leucine zipper transcription factor PtFD1, which interacts with FT, abolishes growth cessation and bud formation induced by SD in Populus[4]. Low expression levels of PHYA and CENTRORADIALIS-LIKE 1/TERMINAL FLOWER 1 (CENL1/TFL1) in rib meristem induce terminal bud www.nature.com/scientificreports formation and subsequent dormancy in Populus under SD5. Over expression of ABSCISIC ACID-INSENSITIVE3 (ABI3), which encodes an ABA-related transcription factor, can induce dormancy in Populus[3]. Array-based gene expression analysis shows that genes in GA, ethylene, auxin and ABA signalling pathways are regulated in bud dormancy in grape[9]. Dormancy release is regulated by FT and TFL1 during vernalisation, which is reviewed by Brunner et al.26. miRNAs regulate dormancy release after chilling in Populus[27]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
