Development of a citrus genome-wide EST collection and cDNA microarray as resources for genomic studies

A functional genomics project has been initiated to approach the molecular characterization of the main biological and agronomical traits of citrus. As a key part of this project, a citrus EST collection has been generated from 25 cDNA libraries covering different tissues, developmental stages and stress conditions. The collection includes a total of 22,635 high-quality ESTs, grouped in 11,836 putative unigenes, which represent at least one third of the estimated number of genes in the citrus genome. Functional annotation of unigenes which have Arabidopsis orthologues (68% of all unigenes) revealed gene representation in every major functional category, suggesting that a genome-wide EST collection was obtained. A Citrus clementina Hort. ex Tan. cv. Clemenules genomic library, that will contribute to further characterization of relevant genes, has also been constructed. To initiate the analysis of citrus transcriptome, we have developed a cDNA microarray containing 12,672 probes corresponding to 6875 putative unigenes of the collection. Technical characterization of the microarray showed high intra- and inter-array reproducibility, as well as a good range of sensitivity. We have also validated gene expression data achieved with this microarray through an independent technique such as RNA gel blot analysis.

Effect of the Growth Retardant 3,5-Dioxo-4-butyryl-cyclohexane Carboxylic Acid Ethyl Ester, an Acylcyclohexanedione Compound, on Fruit Growth and Gibberellin Content of Pollinated and Unpollinated Ovaries in Pea

Treatment of pollinated pea (Pisum sativum L. cv Alaska, line V1) ovaries with 3,5-dioxo-4-butyryl-cyclohexane carboxylic acid ethyl ester (LAB), an acylcyclohexanedione derivative that competitively inhibits 2-oxoglutarate-dependent gibberellin (GA) dioxygenases, caused a reduction of pod elongation proportional to the amount of inhibitor applied. The effect of LAB was counteracted by GA1 and GA3, and partially by GA20. The inhibitor decreased the contents of GA1 and GA3 (the purported active GAs) and GA8, increased those of GA19 and GA20, and did not affect that of GA29 in both the pod and the developing seeds. These results provide evidence that GA1 and/or GA3 control pod development in pea and show that GA20 is not active per se. In contrast to its effect on pollinated ovaries, LAB promoted parthenocarpic development of unpollinated ovaries, which is associated with an increase of GA1 and GA8 content. The inhibitor enhanced the response of unpollinated ovaries to GA1 and GA20, but it did not alter the response to GA3. LAB is proposed to promote parthenocarpic development and enhance the response to exogenous GAs by blocking the 2[beta]-hydroxylation of GA1 more efficiently than 3[beta]-hydroxylation of GA20.

Expression of the le Mutation in Young Ovaries of Pisum sativum and Its Effect on Fruit Development

The effect of the le mutation on the growth and gibberellin (GA) content of developing fruits was investigated using the near-isogenic lines of Pisum sativum L. 205+ (LeLe) and 205- (lele). Although stem elongation is known to be reduced in 205- plants by approximately 65%, the growth of pods and seeds was unaffected by the le mutation. GA1, GA3, and GA20 stimulated parthenocarpic development of unpollinated ovaries on both 205+ and 205- plants. GA20 was less active on 205- ovaries than on 205+, whereas GA1 had similar, high activity in both lines. The activity of GA3 was even higher than that of GA1 in both lines. Decapitation of 205+ plants induced parthenocarpic development of unpollinated ovaries, but this treatment was much less effective on 205- plants. The contents of GA1 and GA8 in entire ovaries 6 d after anthesis, as well as in the pod and fertilized ovules, were substantially lower in 205- than in 205+ plants, whereas the reverse was true for the levels of GA20 and GA29. These results suggest that 3[beta]-hydroxylation of GA20 to GA1 is reduced in ovaries as well as in vegetative tissues. Thus, the le mutation appears to be expressed in young reproductive organs of the 205- line, even though it does not affect the fruit phenotype. Because the content of GA3 in the ovary was similar in the two lines, one explanation for the normal fruit size in the 205- line is that GA3 is the native regulator of pod growth. Alternatively, sufficient GA1 may still be produced in 205- fruits to maintain normal pod growth.

Gibberellins in developing fruits of Pisum sativum cv. Alaska: Studies on their role in pod growth and seed development

Gibberellins A1, A8, A20 and A29 were identified by capillary gas chromatography-mass spectrometry in the pods and seeds from 5-d-old pollinated ovaries of pea (Pisum sativum cv. Alaska). These gibberellins were also identified in 4-d-old non-developing, parthenocarpic and pollinated ovaries. The level of gibberellin A1 within these ovary types was correlated with pod size. Gibberellin A1, applied to emasculated ovaries cultured in vitro, was three to five times more active than gibberellin A20. Using pollinated ovary explants cultured in vitro, the effects of inhibitors of gibberellin biosynthesis on pod growth and seed development were examined. The inhibitors retarded pod growth during the first 7 d after anthesis, and this inhibition was reversed by simultaneous application of gibberellin A3. In contrast, the inhibitors, when supplied to 4-d-old pollinated ovaries for 16 d, had little effect on seed fresh weight although they reduced the levels of endogenous gibberellins A20 and A29 in the enlarging seeds to almost zero. Paclobutrazol, which was one of the inhibitors used, is xylem-mobile and it efficiently reduced the level of seed gibberellins without being taken up into the seed. In intact fruits the pod may therefore be a source of precursors for gibberellin biosynthesis in the seed. Overall, the results indicate that gibberellin A1, present in parthenocarpic and pollinated fruits early in development, regulates pod growth. In contrast the high levels of gibberellins A20 and A29, which accumulate during seed enlargement, appear to be unnecessary for normal seed development or for subsequent germination.

Differential compartmentation of gibberellin a(1) and its metabolites in vacuoles of cowpea and barley leaves

The metabolism and efflux of gibberellin A(1) (GA(1)) taken up by leaves of cowpea (Vigna sinensis cv. Blackeye pea No. 5), as well as the distribution of GA(1) metabolites in the protoplasts and vacuoles of cowpea and barley (Hordeum vulgare L. cv. Numar), were studied.GA(1) is metabolized rapidly in cowpea leaf discs to products tentatively identified as gibberellin A(8) (GA(8)) and gibberellin A(8) glucoside (GA(8)-glu). After labeling leaf discs with [(3)H]GA(1) for 1 hour, the release of radioactivity from the leaf was followed. Over a 12-hour period, the level of radioisotope in the tissue declined to about 35% of the original, after which no further release was observed. At this time, almost all of the radioactivity remaining in the leaf was GA(8)-glu, while most of the radioactivity which had been released was unmetabolized GA(1).Mesophyll protoplasts and vacuoles were isolated from cowpea and barley leaves previously fed [(3)H]GA(1). These protoplasts retain the ability to metabolize GA(1), indicating that neither the leaf structure nor the cell wall is necessary for this metabolism. A higher proportion of GA(8)-glu was found in the vacuoles relative to the entire protoplasts. The results obtained suggest that GA(1) metabolites are preferentially compartmentalized in the vacuoles relative to GA(1).