Vegetative phase change inPopulus tremula x alba

Abstract

SummaryPlants transition through juvenile and adult phases of vegetative development in a process known as vegetative phase change (VPC). In poplars (genus Populus) the differences between these stages are subtle, making it difficult to determine when this transition occurs. Previous studies of VPC in poplars have relied on plants propagated in vitro, so the normal nature of this process is still unknown.We examined developmental morphology of seed-grown and in vitro derived Populus tremula x alba (clone 717-1B4), and compared the phenotype of these, to plants over- and under-expressing miR156, the master regulator of VPC.In seed-grown plants, most traits changed from node-to-node during the first 3 months of development but remained relatively constant starting around node 25. Most of these traits remained unchanged in clones over-expressing miR156, demonstrating they are regulated by the miR156/SPL pathway. Leaf fluttering--a characteristic of Populus tremula (“quaking aspen”)--is one of these miR156-regulated traits.Vegetative development in plants grown from culture mirrored that of seed-grown plants, allowing direct comparison between plants often used in research and those found in nature. These results provide a foundation for further research on the role of VPC in the ecology and evolution of this economically important genus.

MicroRNA156‐mediated changes in leaf composition lead to altered photosynthetic traits during vegetative phase change

“…Populus tremula x alba line 717 1B4 and two independent miR156 overexpressor lines, 40 and 78, described in Lawrence et al, (2020) were obtained by in vitro propagation and hardened on propagation media as described in Meilan & Ma (2006). Plants were then transplanted to Fafard 2 growing mix (Sangro Horticulture, Massachusetts, USA) in 0.3 L pots in the greenhouse at the University of Pennsylvania (39.…”

“…In P. tremula x alba 717-1B4 and miR156 overexpressor lines leaves 10, 15, 20 and 25 were measured. Leaves 10 and 15 in the wild-type 717-1B4 line were juvenile and leaves 20 and 25 were adult as determined by petiole shape and abaxial trichome density as described in Lawrence et al, (2020). All measured leaves in the miR156 overexpressor lines were juvenile.…”

The carbon economics of vegetative phase change: why plants make juvenile and adult leaves

“…It is unclear why the expected negative relationships between LMA and leaf N or Asat are lacking, as LMA increases during VPC in these species. However, previous work found no phase-specific changes in photosynthetic nitrogen use efficiency (PNUE) (Lawrence et al, 2020), indicating adult leaves somehow compensate for the structural changes that often reduce PNUE in high LMA leaves, potentially through their increased stomatal density which could reduce resistance to CO2 diffusion (Hikosaka, 2004;Feng et al, 2016;Lawrence et al, 2021).…”

“…Populus tremula x alba line 717-1B4 and miR156 overexpressor line 40 described in Lawrence et al, (2021) were obtained by in vitro propagation and hardened on propagation media as described in Meilan & Ma (2006). Plants were then transplanted to Fafard-2 growing mix (Sun Gro Horticulture, Massachusetts, USA) in 0.3-L pots in the greenhouse at the University of Pennsylvania (39.…”

“…For all three species, naturally juvenile and adult leaves in wild-type lines and "juvenilized" leaves, those in miR156 overexpressor lines with a juvenile phenotype at leaf positions that would normally be adult, were sampled. In P. tremula x alba, developmental stage was determined by petiole shape and abaxial trichome density as described in Lawrence et al, (2021). Juvenile leaves were sampled from wild-type node 10 and adult from node 25, and juvenilized leaves were sampled from overexpressor node 25.…”