A Rho Scaffold Integrates the Secretory System with Feedback Mechanisms in Regulation of Auxin Distribution

In plants, auxin distribution and tissue patterning are coordinated via a feedback loop involving the auxin-regulated cell polarity factor ICR1 and the secretory machinery

The bHLH transcription factor SPATULA enables cytokinin signaling, and both activate auxin biosynthesis and transport genes at the medial domain of the gynoecium

[EN] Fruits and seeds are the major food source on earth. Both derive from the gynoecium and, therefore, it is crucial to understand the mechanisms that guide the development of this organ of angiosperm species. In Arabidopsis, the gynoecium is composed of two congenitally fused carpels, where two domains: medial and lateral, can be distinguished. The medial domain includes the carpel margin meristem (CMM) that is key for the production of the internal tissues involved in fertilization, such as septum, ovules, and transmitting tract. Interestingly, the medial domain shows a high cytokinin signaling output, in contrast to the lateral domain, where it is hardly detected. While it is known that cytokinin provides meristematic properties, understanding on the mechanisms that underlie the cytokinin signaling pattern in the young gynoecium is lacking. Moreover, in other tissues, the cytokinin pathway is often connected to the auxin pathway, but we also lack knowledge about these connections in the young gynoecium. Our results reveal that cytokinin signaling, that can provide meristematic properties required for CMM activity and growth, is enabled by the transcription factor SPATULA (SPT) in the medial domain. Meanwhile, cytokinin signaling is confined to the medial domain by the cytokinin response repressor ARABIDOPSIS HISTIDINE PHOSPHOTRANSFERASE 6 (AHP6), and perhaps by ARR16 (a type-A ARR) as well, both present in the lateral domains (presumptive valves) of the developing gynoecia. Moreover, SPT and cytokinin, probably together, promote the expression of the auxin biosynthetic gene TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS 1 (TAA1) and the gene encoding the auxin efflux transporter PIN-FORMED 3 (PIN3), likely creating auxin drainage important for gynoecium growth. This study provides novel insights in the spatiotemporal determination of the cytokinin signaling pattern and its connection to the auxin pathway in the young gynoecium.IRO, VMZM, HHU and PLS were supported by the Mexican National Council of Science and Technology (CONACyT) with a PhD fellowship (210085, 210100, 243380 and 219883, respectively). Work in the SDF laboratory was financed by the CONACyT grants CB-2012-177739, FC-2015-2/1061, and INFR-2015-253504, and NMM by the CONACyT grant CB-2011-165986. SDF, CF and LC acknowledge the support of the European Union FP7-PEOPLE-2009-IRSES project EVOCODE (grant no. 247587) and H2020-MSCARISE-2015 project ExpoSEED (grant no. 691109). SDF also acknowledges the Marine Biological Laboratory (MBL) in Woods Hole for a scholarship for the Gene Regulatory Networks for Development Course 2015 (GERN2015). IE acknowledges the International European Fellowship-METMADS project and the Universita degli Studi di Milano (RTD-A; 2016). Research in the laboratory of MFY was funded by NSF (grant IOS-1121055), NIH (grant 1R01GM112976-01A1) and the Paul D. Saltman Endowed Chair in Science Education (MFY). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Reyes Olalde, J.; Zuñiga, V.; Serwatowska, J.; Chávez Montes, R.; Lozano-Sotomayor, P.; Herrera-Ubaldo, H.; Gonzalez Aguilera, K.... (2017). The bHLH transcription factor SPATULA enables cytokinin signaling, and both activate auxin biosynthesis and transport genes at the medial domain of the gynoecium. PLoS Genetics. 13(4):1-31. https://doi.org/10.1371/journal.pgen.1006726S131134Reyes-Olalde, J. I., Zuñiga-Mayo, V. M., Chávez Montes, R. A., Marsch-Martínez, N., & de Folter, S. (2013). Inside the gynoecium: at the carpel margin. Trends in Plant Science, 18(11), 644-655. doi:10.1016/j.tplants.2013.08.002Alvarez-Buylla, E. 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Radial growth of woody species in the conditions of high anthropogenic load in the city of Krasnoyarsk

The dynamics of radial growth of tree stem developing in changing conditions of the city of Krasnoyarsk was studied. For Krasnoyarsk, The problem of creating an environment favorable for people living in Krasnoyarsk is an urgent issue and its integral part is deveping green areas to protect the environment Eight tree species were used to improve the landscape of the city of Krasnoyarsk: Scotch pine Pinus sylvestris L., Colorado spruce Picea pungens Engelm., drooping birch Betula pendula Roth., Siberian elm Ulmus pumila L., balsam poplar Populus balsamifera L., mountain ash Sorbus aucuparia L., Maak bird cherry tree Padus maackii Rupr., and dwarf apple tree Malus baccata (L.) Borkh. The width of the radial growth of the stems was measured during the lifetime of the model trees and the averaged growth paths were obtained for the five sample plots, showing different levels of contamination. On heavily contaminated sample plots, the Siberian elm, balsam poplar, Maak bird cherry tree and dwarf apple tree throughout their life form relatively narrow annual rings (up to 3 mm). It is concluded that these tree species can be used as indicators of anthropogenic pollution of the sit. Drooping birch, Siberian elm, Maak bird cherry tree, and dwarf apple tree on sites with a high level of contamination are characterized by high rate of decrease in the width of annual rings with aging, which shortens the effective life of these plants. Based on the results obtained, preliminary recommendations on the use of the tree species in the urban environment were formulated, taking into account the characteristics of their growth

Variability of the tree-rings structure of Gmelin’s larch at northern tree line (peninsula of Taymyr)

The study of tree-ring cell structure changes as the result of tree adaptation to varying environmental conditions becomes increasingly important to predict future vegetation shifts under projected climate changes. The estimate of intrapopulation annual variability of wood anatomy characteristics is particularly informative. It helps to divide the contribution of different ecological factors to total features dispersion. In this work, a comparative analysis of individual and climatic variability of tree ring structure characteristics of Gmelin’s larch Larix gmelinii (Rupr.) growth within northernmost forest was carried out. The trees from forest-tundra boundary has greater radial growth intensity, forms the bigger conductive zone in rings with wider mean lumen area in comparison with trees from closed forest. This result can be explained by adaptive features and height ecological xylem plasticity of larch. The tree rings structure of larch from boundary with tundra is determined by largely current weather conditions. Is because these ones evince high adaptive plasticity on the level of xylem structure. The xylem reflects joint changes of climate factors and local ecological conditions. The trees from closed forest are characterized by larger individual variability. The local conditions in oldest forest (for example, bad hydrothermal soil conditions) inhibit the radial growth and sensitivity to environmental factors. In this case, the trees on individual level are tended to save the normal functioning of water-transport system. The significant differences in ratio individual to climate variability of tree ring structure characteristics can be caused by the different in the level of ecological habitat heterogeneity or the different in the level genetic within-population heterogeneity

BASE-TO-TIP RADIAL GROWTH AND ANATOMICAL STRUCTURE OF STAG-HEADED LARCH TREES ON PERMAFROST: CAUSES AND EMPIRICAL PRIORITIES

In the northern larch forests of Siberia growing on permafrost soils the top drying phenomenon is widely spread. Its causes remain unclear. We suggest that an acute water deficiency in continuous climate warming could trigger the process of top drying in larch trees. In order to validate this hypothesis, dendroclimatic and wood anatomy approaches were used. A comparative analysis of the base-to-tip radial growth dynamics and wood anatomical structure in healthy and stag-headed Gmelin larch trees (Larix gmelinii (Rupr.) Rupr.), growing in the even-aged forest on the permafrost soil of the north-facing slope (64°19′23″ N, 100°13′28″ E) was made. The tree ring width, as well as lumen radial size and wall thickness of tracheids were measured at 1/4, 1/2 and 3/4 of the stem height and 20-25 cm below the top, in 15 healthy and 12 stag-headed trees. Decreasing trends of the aforementioned parameters from tree base to top were found in all the trees, which was especially evident in the stag-headed trees. Wood anatomical structure in the upper part of the stag-headed stems underwent modifications over the last 20 years: there occurred tree ring boundaries became indistinct, disturbance of the tracheid rows, thinning of early- and latewood tracheid walls. Using sliding climate correlations with the indexed radial increments it was found that the trees on the north-facing slope could suffer from water deficiency from the end of May until the late June. The presence of both stag-headed and neighboring healthy trees on the north-facing slope can be explained by high variability of soil hydrothermal growth conditions due to very high spatial mosaic moss-lichen cover, common to the north-facing slopes. The trees, growing in these unfavorable local hydrothermal conditions under continuous climate warming could experience an extremely acute water deficiency, leading to top drying out

Seasonal Sap Flow Dynamics in Larix sibirica Trees Growing in the Krasnoyarsk Forest-Steppe

Проведен анализ сезонной динамики сокодвижения от корней к кроне у деревьев лиственницы сибирской (Larix sibirica Ledeb.), различающихся по скорости радиального роста, произрастающих на территории опорно-экспедиционного пункта ИЛ СО РАН (ОЭП) «Погорельский бор» (Красноярская лесостепь, 56.36° с.ш., 92.95° в.д.). Непрерывные измерения интенсивности стволового сокодвижения в вегетационные сезоны 2014 и 2015 гг. энергобалансовым (THB) методом проведены на двух одновозрастных деревьях, произрастающих на расстоянии 3 м друг от друга, примерно одинаковой высоты, но разного диаметра. Показано, что сезонная динамика интенсивности сокодвижения у деревьев в общем для них временном интервале в пределах сезона роста характеризуется высокой синхронностью (R=0.77–0.94) при значительной разнице абсолютных значений. С применением эколого-физиологической BS- модели, верифицированной по динамике сокодвижения, была рассчитана суточная и сезонная динамика транспирации. Количество транспортируемой воды в день, приходящееся на дерево, транспирация в день, приходящаяся на единицу листовой поверхности, дефицит влажности воздуха (VPD) и количество осадков в течение сезона роста меняются синхронно, в то же время связь перечисленных показателей с влажностью почвы выражена не столь определенно. Предполагается, что влажность почвы – не определяющий динамику сокодвижения в стволах исследуемых деревьев в означенном месте произрастания фактор, и этим фактором является VPD. На примере двух сезонов вегетации 2014 и 2015 гг. показано, что непрерывные синхронные автоматические измерения интенсивности сокодвижения позволяют исследовать в древостое феноциклы у деревьев с разными скоростями роста и четко устанавливать точные даты начала и окончания их сезона вегетацииSeasonal dynamics of sap flow in the stems of two Siberian larch trees (Larix sibirica Ledeb.) with different radial growth rates were analyzed. The trees grew nearby Pogorelsky Bor research station of Institute of Forest, SB RAS (Krasnoyarsk forest-steppe, 56.36°N, 92.95°E). Intensity of stem sap flow was measured continuously during the vegetation seasons of 2014 and 2015 using the tissue heat balance (THB) method on two individual trees of the same age and height that grew three meters apart and differed in stem diameter (DBH) only. Seasonal dynamics of sap flow intensity of these trees were synchronous (R = 0.77-0.94) within the common vegetation period while the absolute diurnal values differed considerably. The eco-physiological BS-model verified by the data of sap flow measurements allowed to calculate daily and seasonal transpiration dynamics. Seasonal dynamics of sap flow intensity per tree and transpiration per day, and vapor pressure deficit (VPD) as well as seasonal precipitation during the vegetation period were all synchronous. Soil moisture, however, did not show clear correlation with these parameters, thus it may be concluded that it is VPD, but not soil moisture that is the main factor responsible for sap flow intensity in the observed vegetation conditions. The data obtained from the seasons of 2014 and 2015 suggest that continuous automatic measurements of sap flow intensity allow to study phenocycles in trees with various growth rates as well as to determine very precisely the start and the end of their vegetation seaso