Interactions among genes regulating ovule development in Arabidopsis thaliana.

The INNER NO OUTER (INO) and AINTEGUMENTA (ANT) genes are essential for ovule integument development in Arabidopsis thaliana. Ovules of ino mutants initiate two integument primordia, but the outer integument primordium forms on the opposite side of the ovule from the normal location and undergoes no further development. The inner integument appears to develop normally, resulting in erect, unitegmic ovules that resemble those of gymnosperms. ino plants are partially fertile and produce seeds with altered surface topography, demonstrating a lineage dependence in development of the testa. ant mutations affect initiation of both integuments. The strongest of five new ant alleles we have isolated produces ovules that lack integuments and fail to complete megasporogenesis. ant mutations also affect flower development, resulting in narrow petals and the absence of one or both lateral stamens. Characterization of double mutants between ant, ino and other mutations affecting ovule development has enabled the construction of a model for genetic control of ovule development. This model proposes parallel independent regulatory pathways for a number of aspects of this process, a dependence on the presence of an inner integument for development of the embryo sac, and the existence of additional genes regulating ovule development.

The Arabidopsis SUPERMAN Gene Mediates Asymmetric Growth of the Outer Integument of Ovules.

Arabidopsis superman (sup, also referred to as floral mutant10) mutants have previously been shown to have flowers with supernumerary stamens and reduced carpels as a result of ectopic expression of the floral homeotic gene APETALA3 (AP3). Here, we report that sup mutations also cause specific alterations in ovule development. Growth of the outer integument of wild-type ovules occurs almost exclusively on the abaxial side of the ovule, resulting in a bilaterally symmetrical hoodlike structure. In contrast, the outer integument of sup mutant ovules grows equally on all sides of the ovule, resulting in a nearly radially symmetrical tubular shape. Thus, one role of SUP is to suppress growth of the outer integument on the adaxial side of the ovule. Genetic analyses showed that the effects of sup mutations on ovule development are independent of the presence or absence of AP3 activity. Thus, SUP acts through different mechanisms in its early role in ensuring proper determination of carpel identity and in its later role in asymmetric suppression of outer integument growth.

Protein Kinases in Zucchini (Characterization of Calcium-Requiring Plasma Membrane Kinases).

Using an in situ phosphorylation assay with zucchini (Cucurbita pepo L. cv Dark Green) seedling tissue, we have identified numerous polypeptides that are capable of acting as protein kinases. Total protein preparations from different organs contain different kinase profiles, but all are within the range of 55 to 70 kD. At least four kinases are associated with highly purified plasma membranes from etiolated zucchini hypocotyls. The major phosphorylated polypeptides from plasma membranes range in apparent molecular mass from 58 to 68 kD. The plasma membrane kinases are activated by micromolar concentrations of calcium and phosphorylate serine, and, to a lesser extent, threonine residues. These characteristics are similar to those of a soluble calcium-dependent protein kinase that has been purified to homogeneity from soybean suspension cultures. Three of the zucchini plasma membrane kinases share antigenic epitopes with the soluble soybean kinase. The presence of kinase activity at different apparent molecular masses may be indicative of separate kinases with similar characteristics. The zucchini hypocotyl protein kinases are not removed from plasma membrane vesicles by 0.5 M NaCl/5 mM ethylenediaminetetraacetate or by detergent concentrations below the critical micelle concentration of two types of detergent. This indicates that the plasma membrane protein kinases are tightly associated with the membrane in zucchini seedlings.

The altered gravitropic response of the lazy-2 mutant of tomato is phytochrome regulated.

Shoots of the lazy-2 (lz-2) gravitropic mutant of tomato (Lycopersicon esculentum Mill.) have a normal gravitropic response when grown in the dark, but grow downward in response to gravity when grown in the light. Experiments were undertaken to investigate the nature of the light induction of the downward growth of lz-2 shoots. Red light was effective at causing downward growth of hypocotyls of lz-2 seedlings, whereas treatment with blue light did not alter the dark-grown (wild-type) gravity response. Downward growth of lz-2 seedlings is greatest 16 h after a 1-h red light irradiation, after which the seedlings begin to revert to the dark-grown phenotype. lz-2 seedlings irradiated with a far-red light pulse immediately after a red light pulse exhibited no downward growth. However, continuous red or far-red light both resulted in downward growth of lz-2 seedlings. Thus, the light induction of downward growth of lz-2 appears to involve the photoreceptor phytochrome. Fluence-response experiments indicate that the induction of downward growth of lz-2 by red light is a low-fluence phytochrome response, with a possible high-irradiance response component.

Alternative RNA splicing that is spatially regulated: generation of transcripts from the Antennapedia gene of Drosophila melanogaster with different protein-coding regions.

We have shown previously that transcription of the Drosophila homeotic gene Antennapedia results in four major RNA species which differ in long 5'- and 3'-untranslated sequences. The protein-coding portion of these transcripts, however, is located in exons common to all. Using RNase protection assays and further cDNA clone isolation, we have now detected two alternative splicing events between exons of this region. These result in four RNA variations which, if translated, would encode a family of Antennapedia proteins. By analyzing transcripts from various developmental stages and isolated tissues, we show that alternative splicing is under strict temporal and spatial regulation. For example, while similar patterns of splicing were found for all wild-type thoracic imaginal disks examined, these differed distinctly from the patterns observed in neural tissues. Our results suggest that individual RNAs may be associated with different biological roles, and provide molecular evidence that the Antennapedia gene is involved in multiple functions.