A non-invasive method to predict drought survival in Arabidopsis using quantum yield under light conditions.

BACKGROUND: Survival rate (SR) is frequently used to compare drought tolerance among plant genotypes. While a variety of techniques for evaluating the stress status of plants under drought stress conditions have been developed, determining the critical point for the recovery irrigation to evaluate plant SR often relies directly on a qualitative inspection by the researcher or on the employment of complex and invasive techniques that invalidate the subsequent use of the tested individuals. RESULTS: Here, we present a simple, instantaneous, and non-invasive method to estimate the survival probability of Arabidopsis thaliana plants after severe drought treatments. The quantum yield (QY), or efficiency of photosystem II, was monitored in darkness (Fv/Fm) and light (Fv'/Fm') conditions in the last phase of the drought treatment before recovery irrigation. We found a high correlation between a plant's Fv'/Fm' value before recovery irrigation and its survival phenotype seven days after, allowing us to establish a threshold between alive and dead plants in a calibration stage. This correlation was maintained in the Arabidopsis accessions Col-0, Ler-0, C24, and Kondara under the same conditions. Fv'/Fm' was then applied as a survival predictor to compare the drought tolerance of transgenic lines overexpressing the transcription factors ATAF1 and PLATZ1 with the Col-0 control. CONCLUSIONS: The results obtained in this work demonstrate that the chlorophyll a fluorescence parameter Fv'/Fm' can be used as a survival predictor that gives a numerical estimate of the Arabidopsis drought SR before recovery irrigation. The procedure employed to get the Fv'/Fm' measurements is fast, non-destructive, and requires inexpensive and easy-to-handle equipment. Fv'/Fm' as a survival predictor can be used to offer an overview of the photosynthetic state of the tested plants and determine more accurately the best timing for rewatering to assess the SR, especially when the symptoms of severe dehydration between genotypes are not contrasting enough to identify a difference visually.

ROOT PENETRATION INDEX 3, a major quantitative trait locus associated with root system penetrability in Arabidopsis.

Soil mechanical impedance precludes root penetration, confining root system development to shallow soil horizons where mobile nutrients are scarce. Using a two-phase-agar system, we characterized Arabidopsis responses to low and high mechanical impedance at three root penetration stages. We found that seedlings whose roots fail to penetrate agar barriers show a significant reduction in leaf area, root length, and elongation zone and an increment in root diameter, while those capable of penetrating show only minor morphological effects. Analyses using different auxin-responsive reporter lines, exogenous auxins, and inhibitor treatments suggest that auxin responsiveness and PIN-mediated auxin distribution play an important role in regulating root responses to mechanical impedance. The assessment of 21 Arabidopsis accessions revealed that primary root penetrability varies widely among accessions. To search for quantitative trait loci (QTLs) associated to root system penetrability, we evaluated a recombinant inbred population derived from Landsberg erecta (Ler-0, with a high primary root penetrability) and Shahdara (Sha, with a low primary root penetrability) accessions. QTL analysis revealed a major-effect QTL localized in chromosome 3, ROOT PENETRATION INDEX 3 (q-RPI3), which accounted for 29.98% (logarithm of odds=8.82) of the total phenotypic variation. Employing an introgression line (IL-321) with a homozygous q-RPI3 region from Sha in the Ler-0 genetic background, we demonstrated that q-RPI3 plays a crucial role in root penetrability. This multiscale study reveals new insights into root plasticity during the penetration process in hard agar layers, natural variation, and genetic architecture behind primary root penetrability in Arabidopsis.

Regulatory network analysis reveals novel regulators of seed desiccation tolerance in Arabidopsis thaliana.

Desiccation tolerance (DT) is a remarkable process that allows seeds in the dry state to remain viable for long periods of time that in some instances exceed 1,000 y. It has been postulated that seed DT evolved by rewiring the regulatory and signaling networks that controlled vegetative DT, which itself emerged as a crucial adaptive trait of early land plants. Understanding the networks that regulate seed desiccation tolerance in model plant systems would provide the tools to understand an evolutionary process that played a crucial role in the diversification of flowering plants. In this work, we used an integrated approach that included genomics, bioinformatics, metabolomics, and molecular genetics to identify and validate molecular networks that control the acquisition of DT in Arabidopsis seeds. Two DT-specific transcriptional subnetworks were identified related to storage of reserve compounds and cellular protection mechanisms that act downstream of the embryo development master regulators LEAFY COTYLEDON 1 and 2, FUSCA 3, and ABSCICIC ACID INSENSITIVE 3. Among the transcription factors identified as major nodes in the DT regulatory subnetworks, PLATZ1, PLATZ2, and AGL67 were confirmed by knockout mutants and overexpression in a desiccation-intolerant mutant background to play an important role in seed DT. Additionally, we found that constitutive expression of PLATZ1 in WT plants confers partial DT in vegetative tissues.