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Low Temperature Affects Stem Cell Maintenance in Brassica oleracea Seedlings.

ABSTRACT: Most of the above ground tissues in higher plants originate from stem cells located in the shoot apical meristem (SAM). Several plant species can suffer from spontaneous stem cell arrest resulting in lack of further shoot development. In Brassica oleracea this SAM arrest is known as blindness and occurs in an unpredictable manner leading to considerable economic losses for plant raisers and farmers. Detailed analyses of seedlings showed that stem cell arrest is triggered by low temperatures during germination. To induce this arrest reproducibly and to study the effect of the environment, an assay was developed. The role of genetic variation on the susceptibility to develop blind seedlings was analyzed by a quantitative genetic mapping approach, using seeds from a double haploid population from a cross between broccoli and Chinese kale, produced at three locations. The analysis revealed, besides an effect of the seed production location, a region on linkage group C3 associated with blindness sensitivity. A subsequent dynamic genome-wide transcriptome analysis resulted in the identification of around 3000 differentially expressed genes early after blindness induction. A large number of cell cycle genes were en masse induced early during the development of blindness, whereas shortly after, all were down-regulated. This miss-regulation of core cell cycle genes is accompanied with a strong reduction of cells reaching the DNA replication phase. From the differentially expressed genes, 90 were located in the QTL region C3. Among them are two genes belonging to the MINICHROMOSOMAL MAINTENANCE gene family, known to be involved in DNA replication, a RETINOBLASTOMA-RELATED gene, a key regulator for cell cycle initiation, and several MutS homologs genes, involved in DNA repair. These genes are potential candidates for being involved in the development of blindness in Brassica oleracea sensitive genotypes.

SUBMITTER: de Jonge J

PROVIDER: S-EPMC4896912 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Brassica oleracea cultivars include important vegetable and forage crops grown worldwide, whereas the wild counterpart occurs naturally on European sea cliffs. Domestication and selection processes have led to phenotypic and genetic divergence between domesticated plants and their wild ancestors that inhabit coastal areas and are exposed to saline conditions. Salinity is one of the most limiting factors for crop production. However, little is known about how salinity affects plants in relation to domestication of B. oleracea. The objective of this study was to determine the influence of domestication status (wild, landrace or cultivar) on the response of different B. oleracea crops to salinity, as measured by seed germination, plant growth, water content and mineral concentration parameters at the seedling stage. For this purpose, two independent pot experiments were conducted with six accessions of B. oleracea, including cabbage (group capitata) and kale (group acephala), in a growth chamber under controlled environmental conditions. In both taxonomic groups, differences in domestication status and salt stress significantly affected all major process such as germination, changes in dry matter, water relations and mineral uptake. In the acephala experiment, the domestication × salinity interaction significantly affected water content parameters and shoot Na+ allocation. At early stages of development, wild plants are more succulent than cultivated plants and have a higher capacity to maintain lower Na+ concentrations in their shoots in response to increasing levels of salinity. Different responses of domesticated and cultivated accessions in relation to these traits indicated a high level of natural variation in wild B. oleracea. Exclusion of Na+ from shoots and increasing succulence may enhance salt tolerance in B. oleracea exposed to extreme salinity in the long term. The wild germplasm can potentially be used to improve the salt tolerance of crops by the identification of useful genes and incorporation of these into salinity-sensitive cultivars.

Project description:Plants, although sessile, can reorient growth axes in response to changing environmental conditions. Phototropism and gravitropism represent adaptive growth responses induced by changes in light direction and growth axis orientation relative to gravitational direction, respectively. The nearly 80-year-old Cholodny-Went theory Went, F.W. & Thimann, K.V. Phytohormones (1937) (Macmillan, New York) predicts that formation of a gradient of the plant morphogen auxin is central to the establishment of tropic curvature. Loss of tropic responses in seedling stems of Arabidopsis thaliana mutants lacking the auxin-regulated transcriptional activator NPH4/ARF7 has further suggested that a gradient of gene expression represents an essential output from the auxin gradient. Yet, the molecular identities of such output components, which are likely to encode proteins directly involved in growth control, have remained elusive. Here we report the discovery of a suite of tropic stimulus-induced (TSI) genes in Brassica oleracea that are responsive to an auxin gradient, and exhibit morphologically graded expression concomitant with, or before, observable curvature responses. These results provide compelling molecular support for the Cholodny-Went theory, and suggest that morphologically-graded transcription represents an important mechanism for interpreting tropically-stimulated gradients of auxin. Intriguingly, two of the TSI genes, EXPA1 and EXPA8, encode enzymes involved in cell wall extension, a response prerequisite for differential growth leading to curvatures, and are upregulated prior to curvature in the flank that will elongate. This observation suggests that morphologically-graded transcription likely leads to the graded expression of proteins whose activities can directly regulate the establishment and modulation of tropic curvatures. Experiment Overall Design: A 15Â° ophthalmic scalpel (Feather, Osaka, Japan) was used to isolate tissue flanks (~1 cm in length, see Fig. 1A) from etiolated B. oleracea seedlings that had received one of three treatments: 1) a mock stimulation; 2) a 2 h phototropic stimulation; or 3) a 2 h gravitropic stimulation. Only the outer third of the hypocotyl was collected for each flank section, and opposing flanks were collected into separate pools. Hence there were five distinct tissue samples (two flanks for each of two tropic stimulations plus one set of control flanks) with each sample being generated and collected in triplicate for a total of fifteen biological samples. Tissue flanks were immediately quick frozen in liquid N2 and stored at â80Â°C until RNAs were isolated. Total RNA was extracted from frozen tissue using the RNeasy kit (Qiagen, Valencia, CA), followed by cRNA synthesis (ENZO Diagnostics, Farmingdale, NY). cRNA probe generation, as well as microarray hybridization, washing and scanning were performed as described by manufacturer protocols (Affymetrix, Santa Clara, CA).

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Low Temperature Affects Stem Cell Maintenance in Brassica oleracea Seedlings.

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