Genotypic recognition and spatial responses by rice roots

Abstract

Root system growth and development is highly plastic and is influenced by the surrounding environment. Roots frequently grow in heterogeneous environments that include interactions from neighboring plants and physical impediments in the rhizosphere. To investigate how planting density and physical objects affect root system growth, we grew rice in a transparent gel system in close proximity with another plant or a physical object. Root systems were imaged and reconstructed in three dimensions. Root-root interaction strength was calculated using quantitative metrics that characterize the extent to which the reconstructed root systems overlap each other. Surprisingly, we found the overlap of root systems of the same genotype was significantly higher than that of root systems of different genotypes. Root systems of the same genotype tended to grow toward each other but those of different genotypes appeared to avoid each other. Shoot separation experiments excluded the possibility of aerial interactions, suggesting root communication. Staggered plantings indicated that interactions likely occur at root tips in close proximity. Recognition of obstacles also occurred through root tips, but through physical contact in a size-dependent manner. These results indicate that root systems use two different forms of communication to recognize objects and alter root architecture: root-root recognition, possibly mediated through root exudates, and root-object recognition mediated by physical contact at the root tips. This finding suggests that root tips act as local sensors that integrate rhizosphere information into global root architectural changes.3D reconstruction | imaging | kin recognition P lants interact with the environment in a number of ways (1, 2).Aboveground tissues may identify volatile cues that provide information about their neighbors (3, 4) and detect irradiance, directional light, and light quality (5), whereas belowground tissues, such as roots, can detect changes in soil moisture, nutrient availability, and physical obstacles (6-8). Plants not only detect but also respond to changes in their environment, exhibiting adaptation in their morphology and physiology in response to environmental stimuli (9-14), such as alteration in total root length, root system volume, and root depth (15,16). Phenotypic plasticity of plants in response to environmental heterogeneity may have consequences for plant fitness.Communication among plants is mediated by interactions that take place aboveground (17, 18) and belowground (2,(19)(20)(21). Aboveground interactions have been studied in greater detail, in part because of the accessibility of aerial tissue. However, there is growing interest in root-system architecture and its effect on plant function and fitness (12, 15). Studies of root-system architecture suggest that root systems develop differently in the presence of other root systems. For example, when exposed to the roots of a neighboring plant, common bean plants altered the vertical and horizontal distribution of roo...

Quantitative Variation in Responses to Root Spatial Constraint within Arabidopsis thaliana

“…One possible explanation arises from reports of chemical signals, such as secondary metabolites or proteins, in root exudates that mediate how a plant root interacts with its soil environment (de Kroon, 2007;Semchenko et al, 2008;Biedrzycki et al, 2010;Badri et al, 2012;Padilla et al, 2013). This agrees with evidence that roots respond to neighboring roots in a genotype-dependent manner, wherein roots of the same genotypes overlapped better, while roots of different genotypes avoided each other potentially via chemical signals (Fang et al, 2013). However, the specific molecular mechanisms involved in these processes and how they influence foliar growth are poorly understood.…”

“…Recent studies using rhizotron imaging, in which special pots are used to allow direct visualization of the roots, of roots grown in soil or artificial media showed that roots perceive the proximity to neighbors and alter their foraging behavior and architecture (Hodge, 2004;Cahill et al, 2010;Nord et al, 2011;Fang et al, 2013). While nutrient depletion is thought to be a key signal for altered root foraging in competitive environments, recent studies have shown that neighboring roots can also trigger changes in root architecture independently of nutrient competition (Padilla et al, 2013).…”

Self-discrimination in the tendrils of the vine Cayratia japonica is mediated by physiological connection

“…Root self-discrimination and its consequences for underground competition have been reported [7,9,10,34]. However, the role of self-discrimination in above-ground interactions has largely been ignored (but see [35] for the effect of kin discrimination on above-ground traits).…”

“…Root discrimination allows plants to change their root allocation and morphology in response to either self or non-self neighbours [6][7][8][9][10][11][12]. Root discrimination is thought to be mediated by environmentally based physiological coordination rather than by genotype-specific differences as in self-incompatibility and immune systems [7][8][9] (however, see [10]). For example, Gruntman & Novoplansky [9] have demonstrated that clones derived from the same plant become related to each other as genetic aliens after temporal separation.…”

Kin recognition in Setaria italica under the condition of root segregation

“…, 适合度增加 (Tonsor, 1989)。植物的这种行为可以用亲缘选择理 论来解释, 基因上相似度高的个体间可以通过相互 合作减少用于竞争的资源消耗, 从而将更多的资源 投资于繁殖并增加适合度 (Hamilton, 1964a(Hamilton, , 1964bAxelrod & Hamilton, 1981)。当植物的邻居为亲缘株 时, 亲缘选择和生态位分化可能同时起作用, 且两 者作用于同一个过程 (File et al, 2012; Chen et al, 2012;File et al, 2012;Dudley et al, 2013;李洁等, 2014)。目前, 有关植物 亲缘识别的一些研究关注邻株身份如何影响基于植 物繁殖表现的适合度 (Mohana et al, 2001;Milla et al, 2009Milla et al, , 2012Bhatt et al, 2011;Biernaskie, 2011), 另一些关注不同邻株身份对竞争性状及其生物量分 配的影响 (Dudley & File, 2007;Murphy & Dudley, 2009;Bhatt et al, 2011;Lepik et al, 2012;Dudley et al, 2013;Fang et al, 2013;Mercer & Eppley, 2014;Semchenko et al, 2014)。另 外, 地下部分竞争信号在植物身份识别过程中所扮 演的角色得到较多的关注 (Dudley & File, 2007;Murphy & Dudley, 2009;Bhatt et al, 2011;Lepik et al, 2012;Dudley et al, 2013;Fang et al, 2013;Mercer & Eppley, 2014;Semchenko et al, 2014), 少量的研究表明地上部分 竞争信号在植物身份识别过程中也扮演着一定的角 色 (Crepy & Casal, 2015) Chen et al, 2012;Bais, 2015;Crepy & Casal, 2015) ind.·m -2 , 即每小区25株, 植株间距10 cm; 低密度 为36 ind.·m -2 , 即每小区9株, 植株间距16.7 cm。 Fig. 2 Effects of neighbor identity on the morphology and biomass allocation of Setaria italica (mean ± SE).…”