Decoding Gene Networks Modules That Explain the Recovery of Hymenoglossum cruentum Cav. After Extreme Desiccation.

Hymenoglossum cruentum (Hymenophyllaceae) is a poikilohydric, homoiochlorophyllous desiccation-tolerant (DT) epiphyte fern. It can undergo fast and frequent dehydration-rehydration cycles. This fern is highly abundant at high-humidity/low-light microenvironments within the canopy, although rapid changes in humidity and light intensity are frequent. The objective of this research is to identify genes associated to desiccation-rehydration cycle in the transcriptome of H. cruentum to better understand the genetic dynamics behind its desiccation tolerance mechanism. H. cruentum plants were subjected to a 7 days long desiccation-rehydration process and then used to identify key expressed genes associated to its capacity to dehydrate and rehydrate. The relative water content (RWC) and maximum quantum efficiency (F v/F m) of H. cruentum fronds decayed to 6% and 0.04, respectively, at the end of the desiccation stage. After re-watering, the fern showed a rapid recovery of RWC and F v/F m (ca. 73% and 0.8, respectively). Based on clustering and network analysis, our results reveal key genes, such as UBA/TS-N, DYNLL, and LHC, orchestrating intracellular motility and photosynthetic metabolism; strong balance between avoiding cell death and defense (CAT3, AP2/ERF) when dehydrated, and detoxifying pathways and stabilization of photosystems (GST, CAB2, and ELIP9) during rehydration. Here we provide novel insights into the genetic dynamics behind the desiccation tolerance mechanism of H. cruentum.

A comparative gene co-expression analysis using self-organizing maps on two congener filmy ferns identifies specific desiccation tolerance mechanisms associated to their microhabitat preference.

BACKGROUND: Filmy-ferns (Hymenophyllaceae) are poikilohydric, homoiochlorophyllous desiccation-tolerant (DT) epiphytes. They can colonize lower and upper canopy environments of humid forest. Filmy-ferns desiccate rapidly (hours), contrasting with DT angiosperms (days/weeks). It has been proposed that desiccation tolerance in filmy-ferns would be associated mainly with constitutive features rather than induced responses during dehydration. However, we hypothesize that the inter-specific differences in vertical distribution would be associated with different dynamics of gene expression within the dehydration or rehydration phases. A comparative transcriptomic analysis with an artificial neural network was done on Hymenophyllum caudiculatum (restricted to lower canopy) and Hymenophyllum dentatum (reach upper canopy) during a desiccation/rehydration cycle. RESULTS: Raw reads were assembled into 69,599 transcripts for H. dentatum and 34,726 transcripts for H. caudiculatum. Few transcripts showed significant changes in differential expression (DE). H. caudiculatum had ca. twice DE genes than H. dentatum and higher proportion of increased-and-decreased abundance of genes occurs during dehydration. In contrast, the abundance of genes in H. dentatum decreased significantly when transitioning from dehydration to rehydration. According to the artificial neural network results, H. caudiculatum enhanced osmotic responses and phenylpropanoid related pathways, whilst H. dentatum enhanced its defense system responses and protection against high light stress. CONCLUSIONS: Our findings provide a deeper understanding of the mechanisms underlying the desiccation tolerance responses of two filmy ferns and the relationship between the species-specific response and the microhabitats these ferns occupy in nature.

Manganese toxicity amelioration by phosphorus supply in contrasting Mn resistant genotypes of ryegrass.

We evaluated whether phosphorus (P) ameliorates manganese (Mn) excess harmful effects on photosynthetic performance, growth, oxidative stress, and antioxidants in ryegrass. Two perennial ryegrass genotypes, Banquet-II as Mn-resistant and One-50 as Mn-sensitive genotype, were growth under hydroponic conditions subjected to increased P (25, 50, 100, 200 and 400 µM), excess (750 µM) and sufficient Mn (2.4 µM) for 15 days. Growth rate, lipid peroxidation (LP), enzymatic and non-enzymatic antioxidants, photosynthetic parameters, and pigments were determined. Significant reduction of photosynthesis and growth in One-50 was observed under Mn-excess combined with low and adequate P, recovering under greater P-doses. The P concentration of both genotypes was enhanced towards increased P-supply, regardless of Mn treatments. Shoots Mn-concentration remained constant in both genotypes under Mn-excess, independently of P-levels; meanwhile, Banquet-II roots Mn-concentration increased 23% by P-supply. Furthermore, Banquet-II roots showed higher superoxide dismutase (SOD) activity than One-50, which increased towards the highest P dose under sufficient and excess of Mn. A high dose of phosphorus amendment alleviated Mn-toxicity in Mn-sensitive genotype (One-50). Besides, in the Mn-resistant genotype, enhanced plant performance is highlighted, explained by a high Mn-accumulation in roots and increased SOD activity, decreasing Mn translocation to shoots and therefore protecting the photosynthetic apparatus.

Physiological traits and Mn transporter genes expression in ryegrass genotypes under increasing Mn at short-term.

We studied physiological traits and Mn transporter genes expression in ryegrass genotypes (One-50, Banquet-II, Halo-AR1 and Nui) under increasing Mn (2.4-750 µM) at short-term (8-24 h) in nutrient solution. An increment in Mn concentration occurred early in roots of all genotypes at increased Mn doses relative to control. Banquet-II and Nui roots showed the greatest Mn concentration at the highest Mn supply. Net photosynthesis (Pn) of Banquet-II and Halo-AR1 were not perturbed by Mn doses, whereas One-50 and Nui, decayed strongly at the highest Mn dose, concomitant with reduced total chlorophyll concentration. A high accumulation of Mn in roots together the maintained Pn under increased Mn doses in Banquet-II and Halo-AR1 suggest a higher Mn resistance of these genotypes. Stomatal conductance (gs) of all genotypes did not vary in presence of Mn. In roots of Banquet-II an augment of lipid peroxidation (LP) by Mn excess was observed earlier decreasing afterwards, being attenuated by the augment of the radical scavenging activity (RSA) and total phenols (TP) of this genotype. Mn concentration and LP in tissues of One-50 and Nui genotypes rose together, may be due to its Mn sensitivity. Differential expression of Mn transporter genes were found in the studied genotypes grown under increasing supplies of Mn, being MTP8.1 expressed in shoots and NRAMP2-like in roots. We concluded that Banquet-II showed greater Mn concentration associated to high roots NRAMP2-like gene expression, without changes in photosynthetic performance. Despite, this genotype showed an increase of LP at the first hours of Mn-excess, it was decreased by the RSA and TP. Halo-AR1 appears to be Mn-resistant in the short-term due to its photosynthetic performance was unchanged by Mn-toxicity, whilst One-50 and Nui were Mn-sensitive.

Physiological and biochemical responses to manganese toxicity in ryegrass (Lolium perenne L.) genotypes.

We studied resistance to manganese (Mn) toxicity under acidic conditions and its relationship with nutrients such as calcium (Ca) and magnesium (Mg) in new perennial ryegrass (Lolium perenne L.) genotypes (One-50, Banquet-II and Halo-AR1) introduced in southern Chile, using the Nui genotype as the reference. Plants were grown in nutrient solution at increased Mn concentrations (0-750 µM) at pH 4.8, and physiological and biochemical features were determined. Under higher Mn concentration, the One-50 genotype had a significantly lower relative growth rate (RGR) of shoots and roots, whereas in the other cultivars this parameter did not change under variable Mn treatments. Increasing the Mn concentration led to an increased Mn concentration in roots and shoots, with Banquet-II and Halo-AR1 having higher Mn in roots than shoots. Shoot Mg and Ca concentrations in all genotypes (except Banquet-II) decreased concomitantly with increasing Mn applications. In contrast to the other genotypes, Banquet-II and Halo-AR1 maintained their net CO2 assimilation rate regardless of Mn treatment, whereas the chlorophyll concentration decreased in all genotypes with the exception of Banquet-II. In addition, lipid peroxidation in Banquet-II roots increased at 150 µM Mn, but decreased at higher Mn concentrations. This decrease was associated with an increase in antioxidant capacity as well as total phenol concentration. Banquet-II and Halo-AR1 appear to be the most Mn-resistant genotypes based on RGR and CO2 assimilation rate. In addition, Mn excess provoked a strong decrease in Ca and Mg concentrations in shoots of the Mn-sensitive genotype, whereas only slight variations in the Mn-resistant genotype were noted. When other evaluated parameters were taken into account, we concluded that among the perennial ryegrass genotypes introduced recently into southern Chile Banquet-II appears to be the most Mn-resistant, followed by Halo-AR1, with One-50 being the most sensitive.