We have isolated the gene for a protein designated CCAl. This protein can bind t o a region of the promoter of an Arabidopsis light-harvesting chlorophyll a/b protein gene, Lhcb7*3, which is necessary for its regulation by phytochrome. The CCAl protein interacted with two imperfect repeats in the Lhcb7*3 promoter, AAA/,AATCT, a sequence that is conserved in Lhcb genes. A region near the N terminus of CCA1, which has some homology t o the repeated sequence found in the DNA binding domain of Myb proteins, is required for binding t o the Lhcb7*3 promoter. Lines of transgenic Arabidopsis plants expressing antisense RNA for CCAl showed reduced phytochrome induction of the endogenous Lhcb7*3 gene, whereas expression of another phytochrome-regulated gene, rbcS-7A, which encodes the small subunit of ribulose-1 ,Bbisphosphate carboxylase/oxygenase, was not affected. Thus, the CCAl protein acts as a specific activator of Lhcb7*3 transcription in response t o brief red illumination. The expression of CCAl RNA was itself transiently increased when etiolated seedlings were transferred t o light. We conclude that the CCAl protein is a key element in the functioning of the phytochrome signal transduction pathway leading t o increased transcription of this Lhcb gene in Arabidopsis.

We have isolated the gene for a protein designated CCA1. This protein can bind to a region of the promoter of an Arabidopsis light-harvesting chlorophyll a/b protein gene, Lhcb1*3, which is necessary for its regulation by phytochrome. The CCA1 protein interacted with two imperfect repeats in the Lhcb1*3 promoter, AAA/cAATCT, a sequence that is conserved in Lhcb genes. A region near the N terminus of CCA1, which has some homology to the repeated sequence found in the DNA binding domain of Myb proteins, is required for binding to the Lhcb1*3 promoter. Lines of transgenic Arabidopsis plants expressing antisense RNA for CCA1 showed reduced phytochrome induction of the endogenous Lhcb1*3 gene, whereas expression of another phytochrome-regulated gene, rbcS-1A, which encodes the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase, was not affected. Thus, the CCA1 protein acts as a specific activator of Lhcb1*3 transcription in response to brief red illumination. The expression of CCA1 RNA was itself transiently increased when etiolated seedlings were transferred to light. We conclude that the CCA1 protein is a key element in the functioning of the phytochrome signal transduction pathway leading to increased transcription of this Lhcb gene in Arabidopsis.

Downy mildew caused by the oomycete pathogen Pseudoperonospora cubensis is a devastating foliar disease of cucurbits worldwide. We previously demonstrated that the wild melon line PI 124111F (PI) is highly resistant to all pathotypes of P. cubensis . That resistance was controlled genetically by two partially dominant, complementary loci. Here, we show that unlike other plant disease resistance genes, which confer an ability to resist infection by pathogens expressing corresponding avirulence genes, the resistance of PI to P. cubensis is controlled by enhanced expression of the enzymatic resistance ( eR ) genes At1 and At2 . These constitutively expressed genes encode the photorespiratory peroxisomal enzyme proteins glyoxylate aminotransferases. The low expression of At1 and At2 in susceptible melon lines is regulated mainly at the transcriptional level. This regulation is independent of infection with the pathogen. Transgenic melon plants overexpressing either of these eR genes displayed enhanced activity of glyoxylate aminotransferases and remarkable resistance against P. cubensis . The cloned eR genes provide a new resource for developing downy mildew-resistant melon varieties.

The gynoecious Cucumis melo (muskmelon) GY-4 (derived from WI-998 after four generations of selfing and selection) was crossed with the monoecious PI124111F or the andromonoecious '36'. The F1 progeny plants from both crosses were all monoecious. The F2 progeny plants of the cross GY-4 × PI12411 IF (gynoecious × monoecious) segregated 12 monoecious: 3 gynomonoecious or trimonoecious: 1 gynoecious, indicating a two recessive gene difference between gynoecy and monoecy. The backcross to the monoecious parent gave rise to monoecious plants, whereas the backcross to the gynoecious parent segregated 2 monoecious: 1 gynomonoecious: 1 gynoecious. The F2 progeny plants of the cross GY-4 × '36' (gynoecious × andromonoecious) segregated 36 monoecious: 12 andromonoecious: 9 gynomonoecious or trimonoecious: 4 hermaphrodite: 3 gynoecious, indicating a three recessive gene difference between the parents. The backcross to the andromonoecious parent segregated 1 monoecious: 1 andromonoecious, whereas that to the gynoecious parent segregated 2 monoecious: 1 gynomonoecious or trimonoecious: 1 gynoecious. The F2 gynoecious plants from the cross GY-4 × '36' segregated in F3 into 4 all progeny gynoecious: 10 mixed progeny of gynoecious (¾) and hermaphrodite (¼) plants. The results suggest that the monoecious, andromonoecious, and gynoecious parents carried the genes AAGGMM, aaGGMM, and AAggmm, respectively, for sex expression. The following phenotype–genotype relationships are proposed for sex expression in muskmelon: monoecious, A-G---; andromonoecious, aaG---; trimonoecious or gynomonoecious, AA-ggM-; hemaphrodite, aagg--; and gynoecious, A-ggmm.Key words: Cucumis melo, femaleness, germ plasm, F1 hybrids, cantaloupe, Cucurbitaceae, sex expression.

Transformation efficiency of melon is low and is still regarded as a challenge. In this paper, the regeneration and transformation response of ‘BU‐21/3′, a newly characterized melon breeding line, is described. The line seems to be superior in this regard to previously evaluated genotypes. Agrobacterium‐mediated delivery of the GUS or GFP reporter genes into cotyledon explants was used to evaluate efficiency of transient and stable transformation. Good transient expression was observed, and stable transformation frequencies of 0.4‐1.5 transgenic shoots per explant were obtained. Transgenic plantlets were transferred to a contained greenhouse as early as 8‐10 weeks after transformation. Transgenic plants are fertile and exhibit a true‐to‐type phenotype. The ‘BU‐21/3’ line may become a useful tool for the facilitation of transgenic breeding in melon.