Genome sequencing and population genomic analyses provide insights into the adaptive landscape of silver birch

Silver birch ($\textit{Betula pendula}$) is a pioneer boreal tree that can be induced to flower within 1 year. Its rapid life cycle, small (440-Mb) genome, and advanced germplasm resources make birch an attractive model for forest biotechnology. We assembled and chromosomally anchored the nuclear genome of an inbred $\textit{B. pendula}$ individual. Gene duplicates from the paleohexaploid event were enriched for transcriptional regulation, whereas tandem duplicates were overrepresented by environmental responses. Population resequencing of 80 individuals showed effective population size crashes at major points of climatic upheaval. Selective sweeps were enriched among polyploid duplicates encoding key developmental and physiological triggering functions, suggesting that local adaptation has tuned the timing of and cross-talk between fundamental plant processes. Variation around the tightly-linked light response genes $\textit{PHYC}$ and $\textit{FRS10}$ correlated with latitude and longitude and temperature, and with precipitation for $\textit{PHYC}$. Similar associations characterized the growth-promoting cytokinin response regulator ARR1, and the wood development genes $\textit{KAK}$ and $\textit{MED5A}$.Birch sequencing was supported by a Finnish Technology Development Agency (TEKES) grant to J.K., Y.H., and P.A. J.K. and Y.H. were supported by the Finnish Centre of Excellence in Molecular Biology of Primary Producers (Academy of Finland CoE program 2014-2019, decision 271832). Y.H. was funded by the Gatsby Foundation and the European Research Council Advanced Investigator Grant SYMDEV. V.A.A. acknowledges support from the US National Science foundation (0922742 and 1442190). J.S. acknowledges a University of Helsinki 3-year grant. A.H.S. and J.T. acknowledge Academy of Finland decision (266430). EST libraries were created with TEKES funding to E.T.P

Photoperiodic control of seasonal growth is mediated by ABA acting on cell-cell communication

In temperate and boreal ecosystems, seasonal cycles of growth and dormancy allow perennial plants to adapt to winter conditions. We show, in hybrid aspen trees, that photoperiodic regulation of dormancy is mechanistically distinct from autumnal growth cessation. Dormancy sets in when symplastic intercellular communication through plasmodesmata is blocked by a process dependent on the phytohormone abscisic acid. The communication blockage prevents growth-promoting signals from accessing the meristem. Thus, precocious growth is disallowed during dormancy. The dormant period, which supports robust survival of the aspen tree in winter, is due to loss of access to growth-promoting signals

Transcription factors PRE3 and WOX11 are involved in the formation of new lateral roots from secondary growth taproot in A. thaliana.

The spatial deployment of lateral roots determines the ability of a plant to interact with the surrounding environment for nutrition and anchorage. This paper shows that besides the pericycle, the vascular cambium becomes active in Arabidopsis thaliana taproot at a later stage of development and is also able to form new lateral roots. To demonstrate the above, we implemented a two-step approach in which the first step leads to development of a secondary structure in A. thaliana taproot, and the second applies a mechanical stress on the vascular cambium to initiate formation of a new lateral root primordium. GUS staining showed PRE3, DR5 and WOX11 signals in the cambial zone of the root during new lateral root formation. An advanced level of wood formation, characterized by the presence of medullar rays, was achieved. Preliminary investigations suggest the involvement of auxin and two transcription factors (PRE3/ATBS1/bHLH135/TMO7 and WOX11) in the transition of some vascular cambium initials from a role as producers of xylem/phloem mother cells to founder cells of a new lateral root primordium.University of Insubria (FAR) EC FP7 Project. Grant Number: ZEPHYR‐308313 Gatsby Foundation. Grant Number: GAT3395/PR3 National Science Foundation Biotechnology and Biological Sciences Research Council. Grant Number: BB/N013158/1 University of Helsinki. Grant Number: 799992091 European Research Council. Grant Number: 323052 Academy of Finland Centre of Excellence programme. Grant Number: 6305303