RESUMO
Plants dedicate a large amount of energy to the regulated production of living cells programmed to separate from roots into the external environment. This unusual process may be worth the cost because it enables the plant to dictate which species will share its ecological niche. For example, border cells can rapidly attract and stimulate growth in some microorganisms and repel and inhibit the growth of others. Such specificity may provide a way to control the dynamics of adjacent microbial populations in the soil to foster beneficial associations and inhibit pathogenic invasion. Plant genes controlling the delivery of border cells and the expression of their unique properties provide tools to genetically engineer plants with altered border cell quality and quantity. Such variants are being used to test the hypothesis that the function of border cells is to protect plant health by controlling the ecology of the root system.
RESUMO
Many plants release large numbers of metabolically active root border cells into the rhizosphere. We have proposed that border cells, cells produced by the root cap meristem that separate from the rest of the root upon reaching the periphery of the cap, are a singularly differentiated part of the root system that modulates the environment of the plant root by producing specific substances to be released into the rhizosphere. Proteins synthesized in border cells exhibit profiles that are very distinct from those of the root tip (root cap, root meristem, and adjacent cells). In vivo-labeling experiments demonstrate that 13% of the proteins that are abundant in preparations from border cells are undetectable in root tip preparations. Twenty-five percent of the proteins synthesized by border cells in a 1-h period are rapidly excreted into the incubation medium. Quantitative variation in levels of specific marker proteins, including glutamine synthetase, heat-shock protein 70, and isoflavone reductase, also occurs between border cells and cells in the root tip. mRNA differential-display assays demonstrate that these large qualitative and quantitative differences in protein expression are correlated with similarly distinct patterns of gene expression. These observations are consistent with the hypothesis that a major switch in gene expression accompanies differentiation into root border cells, as expected for cells with specialized functions in plant development.
RESUMO
Two cDNA clones representing mRNAs, highly expressed in pea root tips, were isolated by mRNA differential display. Ribonuclease protection analyses showed different patterns of expression of these two messages in several pea tissues. Sequence analysis showed that the first clone, PsH1b-40, has 100% homology with a previously isolated H1 histone cDNA, PsH1b. However, it has an additional 30 nt at the 3' end which is absent in PsH1b, suggesting possible multiple polyadenylation sites in the same mRNA. The second clone, PsH1b-41, encodes a deduced 19.5 kDa protein of 185 amino acids with an isoelectric point of 11.5. The putative globular domain of the encoded protein showed 67-71% residue identity with globular domains of 28 kDa pea PsH1b H1 histone and Arabidopsis thaliana H1-1 H1 histone. It has 9 repeating motifs of (T/S)XXK. In the C-terminal domain, there are four lysine-rich repeating motifs of SXK(T/S)PXKKXK which may be involved in chromatin condensation and decondensation. Southern blot analysis of nuclear DNA shows that PsH1-41 belongs to a multigene family.
Assuntos
Histonas/genética , Pisum sativum/genética , Proteínas de Plantas/genética , Sequência de Aminoácidos , Sequência de Bases , Clonagem Molecular , Regulação da Expressão Gênica no Desenvolvimento , Regulação da Expressão Gênica de Plantas , Genes de Plantas , Dados de Sequência Molecular , RNA Mensageiro/genética , Sequências Repetitivas de Ácido Nucleico , Alinhamento de Sequência , Homologia de Sequência de AminoácidosAssuntos
Expressão Gênica , Reação em Cadeia da Polimerase/métodos , RNA Mensageiro/análise , Ribonucleases/metabolismo , Enzimas de Conjugação de Ubiquitina , Northern Blotting/métodos , Primers do DNA/genética , DNA Complementar/genética , DNA de Cadeia Simples/genética , Ligases/genética , Hibridização de Ácido Nucleico , Pisum sativum/enzimologia , Pisum sativum/genética , RNA Antissenso/genética , RNA Mensageiro/genética , Sensibilidade e Especificidade , Transcrição Gênica/genéticaAssuntos
Técnicas Citológicas , Pisum sativum/citologia , Raízes de Plantas/citologia , Pesquisa , EnsinoRESUMO
The complementary DNA (PsU BC4) representing an mRNA encoding an ubiquitin-conjugating enzyme (UBC) of Pisum sativum has been cloned. The coding region is 444 nucleotides (nt) in length and capable of specifying a 16.5-kDa protein of 148 amino acids (aa) with an isoelectric point of 7.95. The deduced aa sequence showed 97% identity with Arabidopsis thaliana AtUBC8-12 families and tomato ERT17, and 80% identity with yeast ScUBC4 and ScUBC5 and Drosophila melanogaster DmUBC4. The active site cysteine (Cys85) found in UBCs so far described is also conserved in the P. sativum sequence.
