Actin microfilaments are involved in the regulation of HVA1 transcript accumulation in drought-treated barley leaves.

Drought is one of the stresses that limit the yield of barley. Despite extensive studies focused on the issue, the molecular mechanism of the response to drought is still not fully understood. In our previous study, we proposed drought-induced signal perception controlled by actin filaments (AFs). To test this hypothesis, we used a chemical inhibitor of AF polarization-latrunculin B. In drought-treated barley leaves, latrunculin B induced AF depolymerization and altered gene expression (mainly those controlling AF formation), notably inhibiting the expression of HVA1, a dehydrin encoding gene whose function in drought tolerance has been widely studied. These results suggest that AFs might be involved in water-deficit signal perception in plant cells.

A Specialized Histone H1 Variant Is Required for Adaptive Responses to Complex Abiotic Stress and Related DNA Methylation in Arabidopsis.

Linker (H1) histones play critical roles in chromatin compaction in higher eukaryotes. They are also the most variable of the histones, with numerous nonallelic variants cooccurring in the same cell. Plants contain a distinct subclass of minor H1 variants that are induced by drought and abscisic acid and have been implicated in mediating adaptive responses to stress. However, how these variants facilitate adaptation remains poorly understood. Here, we show that the single Arabidopsis (Arabidopsis thaliana) stress-inducible variant H1.3 occurs in plants in two separate and most likely autonomous pools: a constitutive guard cell-specific pool and a facultative environmentally controlled pool localized in other tissues. Physiological and transcriptomic analyses of h1.3 null mutants demonstrate that H1.3 is required for both proper stomatal functioning under normal growth conditions and adaptive developmental responses to combined light and water deficiency. Using fluorescence recovery after photobleaching analysis, we show that H1.3 has superfast chromatin dynamics, and in contrast to the main Arabidopsis H1 variants H1.1 and H1.2, it has no stable bound fraction. The results of global occupancy studies demonstrate that, while H1.3 has the same overall binding properties as the main H1 variants, including predominant heterochromatin localization, it differs from them in its preferences for chromatin regions with epigenetic signatures of active and repressed transcription. We also show that H1.3 is required for a substantial part of DNA methylation associated with environmental stress, suggesting that the likely mechanism underlying H1.3 function may be the facilitation of chromatin accessibility by direct competition with the main H1 variants.

Disturbances in production of progesterone and their implications in plant studies.

Progesterone is a mammalian hormone that has also been discovered in plants but its physiological function in plants is not explained. Experiments using inhibitors of progesterone synthesis and binding would be useful in studies on the significance of this compound in plants. Until now, trilostane and mifepristone have been used in medical sciences as progesterone biosynthesis and binding inhibitors, respectively. We tested these synthetic steroids for the first time in plants and found that they reduced the content of progesterone in wheat. The aim of further experiments was to answer whether the potential disturbances in the production/binding of progesterone, influence resistance to environmental stress (drought) and the development of wheat. Inhibitors and progesterone were applied to plants via roots in a concentration of 0.25-0.5mg/l water. Both inhibitors lowered the activity of CO2 binding enzyme (Rubisco) in wheat exposed to drought stress and trilostane additionally lowered the chlorophyll content. However, trilostane-treated plants were rescued by treatment with exogenous progesterone. The inhibitors also modulated the development of winter wheat, which indicated the significance of steroid regulators and their receptors in this process. In this study, in addition to progesterone and its inhibitors, brassinosteroid (24-epibrassinolide) and an inhibitor of biosynthesis of brassinosteroids were also applied. Mifepristone inhibited the generative development of wheat (like 24-epibrassinolide), while trilostane (like progesterone and an inhibitor of biosynthesis of brassinosteroids) stimulated the development. We propose a model of steroid-induced regulation of the development of winter wheat, where brassinosteroids act as inhibitors of generative development, while progesterone or other pregnane derivatives act as stimulators.