Settling for Less: Do Statoliths Modulate Gravity Perception?

Modifications in Ultrastructural Characteristics and Redox Status of Plants under Environmental Stress: A Review

The rate of global environmental change is unprecedented, with climate change causing an increase in the oscillation and intensification of various abiotic stress factors that have negative impacts on crop production. This issue has become an alarming global concern, especially for countries already facing the threat of food insecurity. Abiotic stressors, such as drought, salinity, extreme temperatures, and metal (nanoparticle) toxicities, are recognized as major constraints in agriculture, and are closely associated with the crop yield penalty and losses in food supply. In order to combat abiotic stress, it is important to understand how plant organs adapt to changing conditions, as this can help produce more stress-resistant or stress-tolerant plants. The investigation of plant tissue ultrastructure and subcellular components can provide valuable insights into plant responses to abiotic stress-related stimuli. In particular, the columella cells (statocytes) of the root cap exhibit a unique architecture that is easily recognizable under a transmission electron microscope, making them a useful experimental model for ultrastructural observations. In combination with the assessment of plant oxidative/antioxidative status, both approaches can shed more light on the cellular and molecular mechanisms involved in plant adaptation to environmental cues. This review summarizes life-threatening factors of the changing environment that lead to stress-related damage to plants, with an emphasis on their subcellular components. Additionally, selected plant responses to such conditions in the context of their ability to adapt and survive in a challenging environment are also described.

SCR Suppressor Mutants: Role in Hypocotyl Gravitropism and Root Growth in Arabidopsis thaliana

The SCARECROW (SCR) transcription factor plays a key role in plant growth and development. However, we know very little about the role of SCR regulated pathways in plant development. Here, we used the homozygous scr1 mutant Arabidopsis thaliana (Wassilewskija ecotype), which had a T-DNA insertion in the SCR coding region and lacks a detectable SCR transcript. This scr1 mutant has a determinate mode of root growth, shoot agravitropism and abnormal internal architecture in all organs examined. To screen for mutants that suppress the scr1 abnormal phenotypes, we exposed homozygous scr1 seeds to ethyl methane sulphonate (EMS) mutagen. Upon growth out of these mutagenized seeds, thirteen suppressor mutant-harboring strains were identified. All thirteen suppressor-harboring strains were homozygous for scr1 and lacked the SCR transcript. Ten scr hypocotyl gravitropic suppressor lines showed improved hypocotyl gravitropic response. These ten suppressors fall into six complementation groups suggesting six different gene loci. Similarly, three independent scr root length suppressor lines rescued only the root growth phenotype and fell into three complementation groups, suggesting the involvement of three different gene loci. These suppressors might identify novel functions of the SCR gene in plant development.

LAZY Gene Family in Plant Gravitropism

Adapting to the omnipresent gravitational field was a fundamental basis driving the flourishing of terrestrial plants on the Earth. Plants have evolved a remarkable capability that not only allows them to live and develop within the Earth's gravity field, but it also enables them to use the gravity vector to guide the growth of roots and shoots, in a process known as gravitropism. Triggered by gravistimulation, plant gravitropism is a highly complex, multistep process that requires many organelles and players to function in an intricate coordinated way. Although this process has been studied for several 100 years, much remains unclear, particularly the early events that trigger the relocation of the auxin efflux carrier PIN-FORMED (PIN) proteins, which presumably leads to the asymmetrical redistribution of auxin. In the past decade, the LAZY gene family has been identified as a crucial player that ensures the proper redistribution of auxin and a normal tropic response for both roots and shoots upon gravistimulation. LAZY proteins appear to be participating in the early steps of gravity signaling, as the mutation of LAZY genes consistently leads to altered auxin redistribution in multiple plant species. The identification and characterization of the LAZY gene family have significantly advanced our understanding of plant gravitropism, and opened new frontiers of investigation into the novel molecular details of the early events of gravitropism. Here we review current knowledge of the LAZY gene family and the mechanism modulated by LAZY proteins for controlling both roots and shoots gravitropism. We also discuss the evolutionary significance and conservation of the LAZY gene family in plants.