Altitudinal and climatic associations of seed dormancy and flowering traits evidence adaptation of annual life cycle timing in Arabidopsis thaliana

The temporal control or timing of the life cycle of annual plants is presumed to provide adaptive strategies to escape harsh environments for survival and reproduction. This is mainly determined by the timing of germination, which is controlled by the level of seed dormancy, and of flowering initiation. However, the environmental factors driving the evolution of plant life cycles remain largely unknown. To address this question we have analysed nine quantitative life history traits, in a native regional collection of 300 wild accessions of Arabidopsis thaliana. Seed dormancy and flowering time were negatively correlated, indicating that these traits have coevolved. In addition, environmental–phenotypic analyses detected strong altitudinal and climatic clines for most life history traits. Overall, accessions showing life cycles with early flowering, small seeds, high seed dormancy and slow germination rate were associated with locations exposed to high temperature, low summer precipitation and high radiation. Furthermore, we analysed the expression level of the positive regulator of seed dormancy DELAY OF GERMINATION 1 (DOG1), finding similar but weaker altitudinal and climatic patterns than seed dormancy. Therefore, DOG1 regulatory mutations are likely to provide a quantitative molecular mechanism for the adaptation of A. thaliana life cycle to altitude and climate.Peer Reviewe

Maturação de sementes de tomate em função da ordem de frutificação na planta

A pesquisa teve por objetivos estudar o processo de maturação de sementes de tomate (Lycopersicon lycopersicum L.) buscando caracterizar a maturidade fisiológica das sementes extraídas de frutos colhidos nos racimos 1, 3 e 5, nas posições proximal e distal. Os frutos foram colhidos aos 30, 40, 50, 60, 70, 80 e 90 dias após a antese (DAA), determinando-se também o acúmulo de unidades térmicas, em graus dias (GD), durante esses respectivos intervalos de tempo. Determinou-se o peso de sementes por fruto bem como o peso de matéria seca, germinação, primeira contagem de germinação, porcentagem e índice de velocidade de emergência de plântulas, deterioração controlada e condutividade elétrica. Não houve diferença entre racimos quanto à época da maturidade fisiológica das sementes, que ocorreu cerca de 750 GD ou 75 DAA. A germinação mais elevada ocorreu antes do acúmulo máximo de matéria seca na semente; o máximo vigor ocorreu, quando os frutos se encontravam com 90% do pericarpo vermelho, próximo ou após a máxima matéria seca.This work aimed to study the maturation of tomato (Lycopersicon lycopersicum L.) seeds, characterizing the physiological maturity of seeds extracted from fruits harvested at trusses 1, 3 and 5, at proximal and distal positions. Fruits were harvested at 30, 40, 50, 60, 70, 80 e 90 days after anthesis (DAA). For the same period, the thermal accumulation in heat units (HU) was also registered. Determinations were performed to quantify the total seed weight per fruit, seed moisture content, average dry weight of seeds, germination rate, and vigor (germination first count, controlled deterioration, seedling emergence and electrical conductivity). There were no differences among trusses regarding seed physiological maturity, which was attained at 750 HU or 75 DAA. Maximum seed germination occurred before maximum seed dry weight was achieved, and the highest seed vigor occurred at or after maximum seed dry weight was achieved, when the fruit’s exocarp was 90% red

Temperature fine-tunes Mediterranean Arabidopsis thaliana life-cycle phenology geographically

To understand how adaptive evolution in life-cycle phenology operates in plants, we need to unravel the effects of geographic variation in putative agents of natural selection on life-cycle phenology by considering all key developmental transitions and their co-variation patterns. We address this goal by quantifying the temperature-driven and geographically varying relationship between seed dormancy and flowering time in the annual Arabidopsis thaliana across the Iberian Peninsula. We used data on genetic variation in two major life-cycle traits, seed dormancy (DSDS50) and flowering time (FT), in a collection of 300 A. thaliana accessions from the Iberian Peninsula. The geographically varying relationship between life-cycle traits and minimum temperature, a major driver of variation in DSDS50 and FT, was explored with geographically weighted regressions (GWR). The environmentally varying correlation between DSDS50 and FT was analysed by means of sliding window analysis across a minimum temperature gradient. Maximum local adjustments between minimum temperature and life-cycle traits were obtained in the southwest Iberian Peninsula, an area with the highest minimum temperatures. In contrast, in off-southwest locations, the effects of minimum temperature on DSDS50 were rather constant across the region, whereas those of minimum temperature on FT were more variable, with peaks of strong local adjustments of GWR models in central and northwest Spain. Sliding window analysis identified a minimum temperature turning point in the relationship between DSDS50 and FT around a minimum temperature of 7.2 °C. Above this minimum temperature turning point, the variation in the FT/DSDS50 ratio became rapidly constrained and the negative correlation between FT and DSDS50 did not increase any further with increasing minimum temperatures. The southwest Iberian Peninsula emerges as an area where variation in life-cycle phenology appears to be restricted by the duration and severity of the hot summer drought. The temperature-driven varying relationship between DSDS50 and FT detected environmental boundaries for the co-evolution between FT and DSDS50 in A. thaliana. In the context of global warming, we conclude that A. thaliana phenology from the southwest Iberian Peninsula, determined by early flowering and deep seed dormancy, might become the most common life-cycle phenotype for this annual plant in the region.Peer Reviewe