Systemic signaling in plant gas exchange

As plants are sessile organisms, the ability to adjust and withstand changing environmental conditions is essential for their survival. Systemic long-distance signaling is known to have an important part in plant responses to abiotic and biotic stresses. However, the role of long-distance systemic signaling in the regulation of plant gas exchange is not well understood. This thesis aims to shed light on how plants could utilize systemic signaling mechanisms in the regulation of stomatal conductance and photosynthesis. To facilitate the research I developed a novel method, where the environmental conditions of a single leaf and the rest of seedling can be controlled separately while simultaneously monitoring the rapid changes in leaf gas exchange. The results indicate that in two tree species, Populus tremula x tremuloides and Betula pendula, systemic signals are involved in the fine-tuning of stomatal conductance and photosynthesis in response to step-changes in ambient light levels and CO2 concentration. However, in Arabidopsis thaliana, leaf gas exchange responds to local changes but is not regulated systemically. I also investigated whether systemic signaling is involved in the stomatal and photosynthetic responses of B. pendula under naturally fluctuating environmental conditions. A comparative analysis of the gas exchange parameters of two separate leaves measured simultaneously under pre-set constant conditions and fluctuating ambient conditions revealed that leaves do not only respond to changes in local light levels but also transmit and perceive information on light fluctuations across the canopy. This thesis also provides evidence that the systemic signals are likely perceived directly by the guard cells and that the concurrent systemic changes in photosynthesis are caused by changes in the supply of CO2 through stomata. I suggest that the rapid systemic signals controlling stomatal conductance are transmitted by ROS, Ca2+ or electric waves as these are the only known signaling mechanisms that correspond to the speed and direction of the observed stomatal responses. Furthermore, the studies reported in this thesis indicate that systemic signaling helps plants to coordinate and fine-tune leaf gas exchange under naturally fluctuating light conditions.Koska kasvit eivät pysty liikkumaan, kyky sopeutua ja sietää alati muuttuvia ympäristöolosuhteita on niille elintärkeää. Systeemisellä, solujen välisellä viestinnällä (systeeminen signalointi) tiedetään olevan tärkeä tehtävä kasvien abioottisen ja bioottisen stressivasteen säätelijänä. Tämän pitkän matkan signaloinnin roolia lehtien ja ilmakehän välisen kaasujenvaihdon säätelijänä ei kuitenkaan ole hyvin tutkittu. Tämä väitöskirja pyrkii tuottamaan uutta tietoa systeemisen signaloinnin merkityksestä ilmarakojen konduktanssin ja fotosynteesin säätelijänä. Osana väitöskirjatutkimusta olen kehittänyt uudenlaisen metodin, jonka avulla on mahdollista säädellä ympäristöolosuhteita yhdelle lehdelle sekä muulle taimelle ja samanaikaisesti monitoroida lehden ja ilmakehän välistä vesihöyryn- ja hiilidioksidinvaihtoa. Tällä menetelmällä tehdyt kokeet osoittavat, että systeemiset signaalit välittävät tietoa valo-olosuhteiden ja ilman hiilidioksidipitoisuuden nopeista muutoksista lehtien välillä hybridihaavalla (Populus tremula x tremuloides) ja rauduskoivulla (Betula pendula) mutta ei lituruoholla (Arabidopsis thaliana). Tässä väitöskirjassa tutkin myös pystyvätkö systeemiset signaalit välittämään tietoa luonnollisesta ympäristöolosuhteiden vaihtelusta lehtien välillä ja vaikuttamaan lehtien pinnalla olevien ilmarakojen sekä fotosynteesin säätelyyn rauduskoivulla. Vertailemalla saman taimen kahden eri lehden kaasujenvaihtoparametrejä samanaikaisesti tasaisissa ja vaihtelevissa olosuhteissa sain selville, että ilmaraot eivät ainoastaan kykene aistimaan muuttuvia valo-olosuhteita mutta myös välittämään tietoa muille lehdille sekä tulkitsemaan muista lehdistä tulevia signaaleja. Ilmarakojen säätelyyn vaikuttaa täten paikallisten olosuhteiden lisäksi koko lehvästön kokemat muutokset valo-olosuhteissa. Systeemisiä viestejä kuljettavat signalointimekanismit koostuvat todennäköisesti solusta soluun kulkevista vapaiden happiradikaalien (ROS), kalsiumin (Ca2+) tai sähköaaltojen välittämistä erittäin nopeista signaaleista. Tämän väitöskirjan esittelemän uuden tutkimustiedon pohjalta voidaan todeta, että systeemisten signaalien välittämä tieto koko lehvästön valo-olosuhteista auttaa puita koordinoimaan ja hienosäätämään vesihöyryn ja hiilidioksidin kulkua lehden ja ilmakehän välillä

Systemic signalling in the regulation of stomatal conductance

Peer reviewe

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

Silver birch (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 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 PHYC and FRS10 correlated with latitude and longitude and temperature, and with precipitation for PHYC. Similar associations characterized the growth-promoting cytokinin response regulator ARR1, and the wood development genes KAK and MED5A.Peer reviewe

Author Correction: Genome sequencing and population genomic analyses provide insights into the adaptive landscape of silver birch.

In the version of this article initially published, there was a mistake in the calculation of the nucleotide mutation rate per site per generation: 1 × 10−9 mutations per site per generation was used, whereas 9.5 × 10−9 was correct. This error affects the interpretation of population-size changes over time and their possible correspondence with known geological events, as shown in the original Fig. 4 and supporting discussion in the text, as well as details in the Supplementary Note. Neither the data themselves nor any other results are affected. Figure 4 has been revised accordingly. Images of the original and corrected figure panels are shown in the correction notice

Reactive Oxygen Species, Photosynthesis, and Environment in the Regulation of Stomata

Significance: Stomata sense the intercellular carbon dioxide (CO2) concentration (C-i) and water availability under changing environmental conditions and adjust their apertures to maintain optimal cellular conditions for photosynthesis. Stomatal movements are regulated by a complex network of signaling cascades where reactive oxygen species (ROS) play a key role as signaling molecules. Recent Advances: Recent research has uncovered several new signaling components involved in CO2- and abscisic acid-triggered guard cell signaling pathways. In addition, we are beginning to understand the complex interactions between different signaling pathways. Critical Issues: Plants close their stomata in reaction to stress conditions, such as drought, and the subsequent decrease in C-i leads to ROS production through photorespiration and over-reduction of the chloroplast electron transport chain. This reduces plant growth and thus drought may cause severe yield losses for agriculture especially in arid areas. Future Directions: The focus of future research should be drawn toward understanding the interplay between various signaling pathways and how ROS, redox, and hormonal balance changes in space and time. Translating this knowledge from model species to crop plants will help in the development of new drought-resistant crop species with high yields. Antioxid. Redox Signal. 00, 000-000.Peer reviewe

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

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

Silver birch (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 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 PHYC and FRS10 correlated with latitude and longitude and temperature, and with precipitation for PHYC. Similar associations characterized the growth-promoting cytokinin response regulator ARR1, and the wood development genes KAK and MED5A

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

Abstract Silver birch (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 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 PHYC and FRS10 correlated with latitude and longitude and temperature, and with precipitation for PHYC. Similar associations characterized the growth-promoting cytokinin response regulator ARR1, and the wood development genes KAK and MED5A