Light-modulated seminal wavy roots in rice mediated by nitric oxide-dependent signaling

Ambient temperature regulates root circumnutation in rice through the ethylene pathway: transcriptome analysis reveals key genes involved

Plant roots are constantly prepared to adjust their growth trajectories to avoid unfavorable environments, and their ability to reorient is particularly crucial for survival. Under laboratory conditions, this continuous reorientation of the root tip is manifested as coiling or waving, which we refer to as root circumnutation. However, the effect of ambient temperature (AT) on root circumnutation remains unexplored. In this study, rice seedlings were employed to assess the impact of varying ATs on root circumnutation. The role of ethylene in mediating root circumnutation under elevated AT was examined using the ethylene biosynthesis inhibitor aminooxyacetic acid (AOA) and the ethylene perception antagonist silver thiosulfate (STS). Furthermore, transcriptome sequencing, weighted gene co-expression network analysis, and real-time quantitative PCR were utilized to analyze gene expressions in rice root tips under four distinct treatments: 25°C, 35°C, 35°C+STS, and 35°C+AOA. As a result, genes associated with ethylene synthesis and signaling (OsACOs and OsERFs), auxin synthesis and transport (OsYUCCA6, OsABCB15, and OsNPFs), cell elongation (OsEXPAs, OsXTHs, OsEGL1, and OsEXORDIUMs), as well as the inhibition of root curling (OsRMC) were identified. Notably, the expression levels of these genes increased with rising temperatures above 25°C. This study is the first to demonstrate that elevated AT can induce root circumnutation in rice via the ethylene pathway and proposes a potential molecular model through the identification of key genes. These findings offer valuable insights into the growth regulation mechanism of plant roots under elevated AT conditions.

Evaluating Root Mechanosensing Response in Rice

Unable to move, plants are physically restrained to the place where they grow. Remarkably, plants have developed a myriad of mechanisms to perceive the surrounding environment in order to maximize growth and survival. One of those mechanisms is the ability to perceive mechanical stimulus such as touch (thigmomorphogenesis), in order to adjust growth patterns (in different organs) to either attach to or surround an object. Roots are able to perceive several mechanical forces (e.g., gravity, touch). However, being the "hidden part" of a plant, it is difficult to assess their response to mechanical stimulation. In this chapter, our team presents a simple method to evaluate rice (Oryza sativa L.) root mechanosensing response that can be used to test different conditions (e.g., hormones) affecting rice root response to touch stimulus. This method is affordable to any lab and can be upgraded with a fully automated image recording system. We provide a detailed protocol with several notes for a more comprehensive application.

The light and dark sides of nitric oxide: multifaceted roles of nitric oxide in plant responses to light

Light drives photosynthesis and informs plants about their surroundings. Regarded as a multifunctional signaling molecule in plants, nitric oxide (NO) has been repeatedly demonstrated to interact with light signaling cascades to control plant growth, development and metabolism. During early plant development, light-triggered NO accumulation counteracts negative regulators of photomorphogenesis and modulates the abundance of, and sensitivity to, plant hormones to promote seed germination and de-etiolation. In photosynthetically active tissues, NO is generated at distinct rates under light or dark conditions and acts at multiple target sites within chloroplasts to regulate photosynthetic reactions. Moreover, changes in NO concentrations in response to light stress promote plant defenses against oxidative stress under high light or ultraviolet-B radiation. Here we review the literature on the interaction of NO with the complicated light and hormonal signaling cascades controlling plant photomorphogenesis and light stress responses, focusing on the recently identified molecular partners and action mechanisms of NO in these events. We also discuss the versatile role of NO in regulating both photosynthesis and light-dependent stomatal movements, two key determinants of plant carbon gain. The regulation of nitrate reductase (NR) by light is highlighted as vital to adjust NO production in plants living under natural light conditions.

Different forms of osmotic stress evoke qualitatively different responses in rice

Drought, salinity and alkalinity are distinct forms of osmotic stress with serious impacts on rice productivity. We investigated, for a salt-sensitive rice cultivar, the response to osmotically equivalent doses of these stresses. Drought, experimentally mimicked by mannitol (single factor: osmotic stress), salinity (two factors: osmotic stress and ion toxicity), and alkalinity (three factors: osmotic stress, ion toxicity, and depletion of nutrients and protons) produced different profiles of adaptive and damage responses, both locally (in the root) as well as systemically (in the shoot). The combination of several stress factors was not necessarily additive, and we even observed cases of mitigation, when two (salinity), or three stressors (alkalinity) were compared to the single stressor (drought). The response to combinations of individual stress factors is therefore not a mere addition of the partial stress responses, but rather represents a new quality of response. We interpret this finding in a model, where the output to signaling molecules is not determined by their abundance per se, but qualitatively depends on their adequate integration into an adaptive signaling network. This output generates a systemic signal that will determine the quality of the shoot response to local concentrations of ions.

Light-mediated modulation of helix angle and rate of seminal root tip movement determines root morphology of young rice seedlings

Seminal root growth is one of the factors to determine rice seedling establishment. Our previous reports showed light can induce Z-type wavy root and coiling root morphology in several rice (Oryza sativa L.) varieties, and the regulated Z-type and unregulated coil seminal roots were resulted by different circumnutational trajectories. Moreover, the light-induced seminal root waving was conducted by an NO-dependent signaling pathway. In order to further reveal the difference of root tip movement between straight and wavy seminal roots; here, the root tip movement trajectories of Tainung 67 variety (TNG67; presented straight root in light conditions) and Taichung Native 1 (TCN1; presented Z-type wavy root in light) were recorded and analyzed in both white light and dark (dim far-red light was applied in dark for taking time-lapse photography) conditions. The results showed the root tip movement of both rice varieties in low intensity of dim far-red light conditions were followed the circumnutation path. However, the stimuli of high intensity of white light would increase the root helix angle in TCN1 seedlings but not in TNG67. In addition, slowing down the rate of root helix was induced by white light treatment in TCN1 but not in TNG67 seedlings. In conclusion, changes of TCN1 rice seminal root morphology from straight to wavy type stimulated by light was resulted by both helix angle increasing and circumnutation rate slowing of root tip movement.