Biomedical subjects

James B Reid

Publications and source records attributed to James B Reid.

23 records · Page 2Linked to original sources

PubMed2003

The LKA gene is a BRASSINOSTEROID INSENSITIVE 1 homolog of pea.

Brassinosteroids (BRs) are growth-promoting plant steroid hormones, and in garden pea (Pisum sativum L.), the lka mutant is defective in BR perception. Here, we show that LKA encodes P. sativum BRI1 (PsBRI1), a homolog of BRI1, which is the Arabidopsis leucine-rich repeat receptor-like kinase/BR receptor. PsBRI1 was isolated by screening a pea cDNA library using Arabidopsis BRI1 cDNA as the probe. PsBRI1 is predicted to encode a 1188-amino-acid protein that has 78% similarity with Arabidopsis BRI1. Sequence analysis of PsBRI1 in the lka mutant led to the identification of a missense mutation that converts the highly conserved aspartic acid residue to asparagine, which is located in the leucine-rich repeat, just before the island domain that may bind BR or a BR-protein complex. The mutation identified in PsBRI1 co-segregated with the semi-erectoide lka phenotype. Transcript analysis of LKA/PsBRI1 indicates that it is ubiquitously expressed in pea and that the expression was downregulated by exogenous BR. The lka mutant was then utilized in further studies to analyze the independent actions of BR and gibberellin (GA) through the characterization of BR response on GA mutants and GA response on BR mutants.

Amino Acid Sequence↗

PubMed2003

The pea gene NA encodes ent-kaurenoic acid oxidase.

The gibberellin (GA)-deficient dwarf na mutant in pea (Pisum sativum) has severely reduced internode elongation, reduced root growth, and decreased leaflet size. However, the seeds develop normally. Two genes, PsKAO1 and PsKAO2, encoding cytochrome P450 monooxygenases of the subfamily CYP88A were isolated. Both PsKAO1 and PsKAO2 had ent-kaurenoic acid oxidase (KAO) activity, catalyzing the three steps of the GA biosynthetic pathway from ent-kaurenoic acid to GA(12) when expressed in yeast (Saccharomyces cerevisiae). In addition to the intermediates ent-7alpha-hydroxykaurenoic acid and GA(12)-aldehyde, some additional products of the pea KAO activity were detected, including ent-6alpha,7alpha-dihydroxykaurenoic acid and 7beta-hydroxykaurenolide. The NA gene encodes PsKAO1, because in two independent mutant alleles, na-1 and na-2, PsKAO1 had altered sequences and the five-base deletion in PsKAO1 associated with the na-1 allele cosegregated with the dwarf na phenotype. PsKAO1 was expressed in the stem, apical bud, leaf, pod, and root, organs in which GA levels have previously been shown to be reduced in na plants. PsKAO2 was expressed only in seeds and this may explain the normal seed development and normal GA biosynthesis in seeds of na plants.

Blotting, Northern↗

PubMed2002

Hormone levels and response during de-etiolation in pea.

The objective of this study was to increase our understanding of the hormonal regulation of de-etiolation by investigating endogenous hormone levels and response in etiolated pea ( Pisum sativum L.) seedlings after exposure to continuous white light. Recent reports suggest that de-etiolation may result from the down-regulation of an enzyme in the brassinosteroid (BR) biosynthesis pathway in pea. A subsequent review highlighted the need for direct measurements of BR levels to support this hypothesis. We have shown that endogenous castasterone and 6-deoxocastasterone levels are not greatly reduced after exposure to light; indeed, 6-deoxocastasterone levels were actually increased. Similarly, the elongation response to exogenous brassinolide was greater in plants grown in continuous light, or in dark-grown plants that had been transferred into the light, than in plants that were grown in continuous darkness. These results provide further evidence to suggest that BRs do not negatively regulate de-etiolation in pea. However, changes in the levels of several other hormones have also been implicated in light-regulated development. We have simultaneously quantified indole-3-acetic acid (IAA), gibberellin (GA), and abscisic acid levels in whole seedlings, which revealed a complex pattern of changes in the levels of these substances after exposure to light. The first and most dramatic of these changes was a significant reduction in GA(1) levels, which reached a minimum 8 h after exposure to light. Whilst GA(1) levels rapidly decreased, IAA levels remained unchanged in the short term after exposure to light, suggesting that GA(1) levels may be the primary factor regulating the reduction in elongation growth during de-etiolation. In the long term after exposure to light, IAA levels underwent a transitory increase, which peaked at 48 h, and had abated by 96 h. However, abscisic acid levels remained unchanged in the first 1 h after exposure to light before undergoing a steady decline over time. The relative importance of these changes in mediating light-induced changes in plant morphology is discussed.

Abscisic Acid↗

PubMed2002

Uncoupling brassinosteroid levels and de-etiolation in pea.

The suggestion that brassinosteroids (BRs) have a negative regulatory role in de-etiolation is based largely on correlative evidence, which includes the de-etiolated phenotypes of, and increased expression of light-regulated genes in, dark-grown mutants defective in BR biosynthesis or response. However, we have obtained the first direct evidence which shows that endogenous BR levels in light-grown pea seedlings are increased, not decreased, in comparison with those grown in the dark. Similarly, we found no evidence of a decrease in castasterone (CS) levels in seedlings that were transferred from the dark to the light for 24 h. Furthermore, CS levels in the constitutively de-etiolated lip1 mutant are similar to those in wild-type plants, and are not reduced as is the case in the BR-deficient lkb plants. Unlike lip1, the pea BR-deficient mutants lk and lkb are not de-etiolated at the morphological or molecular level, as they exhibit neither a de-etiolated phenotype or altered expression of light-regulated genes when grown in the dark. Similarly, dark-grown WT plants treated with the BR biosynthesis inhibitor, Brz, do not exhibit a de-etiolated phenotype. In addition, analysis of the lip1lkb double mutant revealed an additive phenotype indicative of the two genes acting in independent pathways. Together these results strongly suggest that BR levels do not play a negative-regulatory role in de-etiolation in pea.

Journal Article↗

PubMed2002

Control of gibberellin levels and gene expression during de-etiolation in pea.

Gibberellin A(1) (GA(1)) levels drop significantly in wild-type pea (Pisum sativum) plants within 4 h of exposure to red, blue, or far-red light. This response is controlled by phytochrome A (phyA) (and not phyB) and a blue light receptor. GA(8) levels are increased in response to 4 h of red light, whereas the levels of GA(19), GA(20), and GA(29) do not vary substantially. Red light appears to control GA(1) levels by down-regulating the expression of Mendel's LE (PsGA3ox1) gene that controls the conversion of GA(20) to GA(1), and by up-regulating PsGA2ox2, which codes for a GA 2-oxidase that converts GA(1) to GA(8). This occurs within 0.5 to 1 h of exposure to red light. Similar responses occur in blue light. The major GA 20-oxidase gene expressed in shoots, PsGA20ox1, does not show substantial light regulation, but does show up-regulation after 4 h of red light, probably as a result of feedback regulation. Expression of PsGA3ox1 shows a similar feedback response, whereas PsGA2ox2 shows a feed-forward response. These results add to our understanding of how light reduces shoot elongation during de-etiolation.

Gene Expression Regulation, Plant↗