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Plants belong to the section Mina showed characteristic petal pigmentation among Ipomoea plants. For example, petals of Ipomoea hederifolia var. lutea display yellow color derived from carotenoids and those of Ipomoea quamoclit display red color derived from pelargonidin-based anthocyanins. In this study, the pigment composition and the expression patterns of genes for pigment biosynthesis in the petals of I. quamoclit and I. hederifolia var. lutea were analyzed to elucidate the crucial factors that determine petal color in section Mina. The petals of white-flowered I. quamoclit lack the ability to synthesize anthocyanins and carotenoids because of the suppression of anthocyanidin synthase (ANS) gene expression and transcriptional down-regulation of multiple carotenogenic genes, respectively. In petals of I. hederifolia var. lutea, the absence of dihydroflavonol 4-reductase (DFR) gene expression is responsible for the lack of anthocyanins. All F1 progeny obtained by interspecies crossing between I. quamoclit and I. hederifolia var. lutea had scarlet petal color produced by a combination of pelargonidin-based anthocyanins and carotenoids. The flavanone 3-hydroxylase gene, DFR, and ANS were expressed in the petals of the F1 progeny. The results suggest that in these section Mina species, the carotenoid-accumulating phenotype in petals is dominant, and that pelargonidin was produced in the F1 progeny by complementary expression of DFR from white-flowered I. quamoclit and ANS from I. hederifolia var. lutea.

It has long been proposed that white-flowered chrysanthemums (Chrysanthemum morifolium Ramat.) have a single dominant gene that inhibits carotenoid formation or accumulation in ray petals. However, the precise function of the proposed gene was unknown. We previously isolated a gene encoding carotenoid cleavage dioxygenase 4, designated CmCCD4a, which is specifically expressed in the ray petals of white-flowered chrysanthemums. Because CmCCD4a was a strong candidate for the single dominant gene, we analyzed the relationship between CmCCD4a expression and carotenoid content in two sets of petal color mutants. Here, we show that CmCCD4a represents a small gene family containing at least four members. Two of them, CmCCD4a-1 and CmCCD4a-2, were highly expressed in ray petals of two taxa with low carotenoid levels. In petal color mutants derived from these taxa, increases in carotenoid levels accompanied decreases in CmCCD4a expression levels in ray petals. Two different circumstances reduced the levels of CmCCD4a expression in the mutants: either a CmCCD4a gene was lost from the genome or the expression of a CmCCD4a gene was suppressed. In the latter case, suppression may be caused by the loss of a function that normally enhances CmCCD4a transcription. A stepwise decrease in the amount of CmCCD4a expression in either L1 or L2 resulted in a corresponding stepwise increase in the carotenoid content in ray petals. From these results, we propose that CmCCD4a expression is the key factor that controls the carotenoid content in ray petals of chrysanthemum.

Late blight, caused by the notorious pathogen Phytophthora infestans, is a devastating disease of potato (Solanum tuberosum) and tomato (Solanum lycopersicum), and during the 1840s caused the Irish potato famine and over one million fatalities. Currently, grown potato cultivars lack adequate blight tolerance. Earlier cultivars bred for resistance used disease resistance genes that confer immunity only to some strains of the pathogen harboring corresponding avirulence gene. Specific resistance gene-mediated immunity and chemical controls are rapidly overcome in the field when new pathogen races arise through mutation, recombination, or migration from elsewhere. A mitogen-activated protein kinase (MAPK) cascade plays a pivotal role in plant innate immunity. Here we show that the transgenic potato plants that carry a constitutively active form of MAPK kinase driven by a pathogen-inducible promoter of potato showed high resistance to early blight pathogen Alternaria solani as well as P. infestans. The pathogen attack provoked defense-related MAPK activation followed by induction of NADPH oxidase gene expression, which is implicated in reactive oxygen species production, and resulted in hypersensitive response-like phenotype. We propose that enhancing disease resistance through altered regulation of plant defense mechanisms should be more durable and publicly acceptable than engineering overexpression of antimicrobial proteins.

Japanese morning glory (Ipomoea nil) is a representative plant lacking a yellow-flowered cultivar, although a few wild Ipomoea species contain carotenoids in their petals such as Ipomoea sp. (yellow petals) and I. obscura (pale-yellow petals). In the present study, carotenoid composition and the expression patterns of carotenogenic genes during petal development were compared among I. nil, I. obscura, and Ipomoea sp. to identify the factors regulating carotenoid accumulation in Ipomoea plant petals. In the early stage, the carotenoid composition in petals of all the Ipomoea plants tested was the same as in the leaves mainly showing lutein, violaxanthin, and beta-carotene (chloroplast-type carotenoids). However, in fully opened flowers, chloroplast-type carotenoids were entirely absent in I. nil, whereas they were present in trace amounts in the free form in I. obscura. At the late stage of petal development in Ipomoea sp., the majority of carotenoids were beta-cryptoxanthin, zeaxanthin, and beta-carotene (chromoplast-type carotenoids). In addition, most of them were present in the esterified form. Carotenogenic gene expression was notably lower in I. nil than in Ipomoea sp. In particular, beta-ring hydroxylase (CHYB) was considerably suppressed in petals of both I. nil and I. obscura. The CHYB expression was found to be significantly high in the petals of Ipomoea sp. during the synthesis of chromoplast-type carotenoids. The expression levels of carotenoid cleavage genes (CCD1 and CCD4) were not correlated with the amount of carotenoids in petals. These results suggest that both I. obscura and I. nil lack the ability to synthesize chromoplast-type carotenoids because of the transcriptional down-regulation of carotenogenic genes. CHYB, an enzyme that catalyses the addition of a hydroxyl residue required for esterification, was found to be a key enzyme for the accumulation of chromoplast-type carotenoids in petals.