Suppressive mechanism of seed coat pigmentation in yellow soybean

In soybean seeds, numerous variations in colors and pigmentation patterns exist, most of which are observed in the seed coat. Patterns of seed coat pigmentation are determined by four alleles (I, iⁱ, i^k and i) of the classically defined I locus, which controls the spatial distribution of anthocyanins and proanthocyanidins in the seed coat. Most commercial soybean cultivars produce yellow seeds with yellow cotyledons and nonpigmented seed coats, which are important traits of high-quality seeds. Plants carrying the I or iⁱ allele show complete inhibition of pigmentation in the seed coat or pigmentation only in the hilum, respectively, resulting in a yellow seed phenotype. Classical genetic analyses of the I locus were performed in the 1920s and 1930s but, until recently, the molecular mechanism by which the I locus regulated seed coat pigmentation remained unclear. In this review, we provide an overview of the molecular suppressive mechanism of seed coat pigmentation in yellow soybean, with the main focus on the effect of the I allele. In addition, we discuss seed coat pigmentation phenomena in yellow soybean and their relationship to inhibition of I allele action.     

Involvement of carbon catabolite repression on regulation of endopolygalacturonase gene expression in citrus fruit

 The Acpg1 gene of Alternaria citri encodes an extracellular endopolygalacturonase that is important for virulence in citrus fruits. Expression of Acpg1 is regulated by substrate induction and carbon catabolite repression. A green fluorescent protein (GFP) gene was employed as a reporter gene to define 813 bases upstream of the translation start site comprising the Acpg1 promoter. This upstream sequence contains five putative binding sequences of catabolite repressive element A (CreA), a cis-acting zinc finger repressor involved in carbon catabolite repression. We constructed each CreA-binding site-deleted Acpg1 promoters with GFP reporter gene and transformed them to A. citri. The construct PGPDL4 deleted from −401 to −813 showed both substrate induction and catabolite repression, whereas PGPDL5 additionally deleted from −1 to −84, including one putative CreA-binding site, resulted in a loss of catabolite repression function. Green fluorescence of PGPDL4 was induced by pectin in the peel but was repressed completely in the juice sac area of citrus fruit. However, green fluorescence of PGPDL5 was induced in both the peel and juice sac area, indicating that repression of Acpg1 in the juice sac area is likely accomplished by carbon catabolite repression. Received: October 4, 2002 / Accepted: October 31, 2002 Acknowledgments The authors thank Drs. D. Cullen, A. Van den Wymelenberg, and J. Andrews, University of Wisconsin, for providing pTEFEGFP containing GFP and Dr. T. Tsuge, Nagoya University, for providing transformation vector pSH75. The nucleotide sequence data of Acpg1 promoter region in the DDBJ, EMBL, and GenBank sequence databases is under accession number AB047543. This research was supported in part by grants to K.A. from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.     

Distribution of avirulence genes <Emphasis Type="Italic">avrA</Emphasis> and <Emphasis Type="Italic">popP1</Emphasis> in 22 Japanese phylotype I strains of <Emphasis Type="Italic">Ralstonia solanacearum</Emphasis>

Sequence analysis of hrp loci and effector genes in the flanking regions showed significantly high similarities between two phylotype I strains of Ralstonia solanacearum, GMI1000 and Japanese strain OE1-1. Further sequence analysis of the distribution of avrA and popP1, known as determinants of a hypersensitive response (HR) induction on Nicotiana tabacum (tobacco), in 22 Japanese phylotype I strains revealed that all strains had one of the two distinct avrA alleles and that 10 strains had an identical popP1 but the other 12 did not. After infiltration of tobacco leaves, more than half of these 22 strains elicited HR. In combination with the ability to induce HR, avrA and popP1 are thus not likely to be the sole determinants of HR in Japanese phylotype I strains.     

Molecular typing of Japanese strains of Ralstonia solanacearum in relation to the ability to induce a hypersensitive reaction in tobacco

The genetic diversity of 120 Ralstonia solanacearum strains isolated from a variety of host plants across Japan was assessed on the basis of hypersensitive response (HR) in tobacco leaves and phylogenetic analyses of endoglucanase gene egl, hrpB, and gyrB. Phylogenetic analysis of egl revealed that only three strains belonged to phylotype IV, and 117 strains belonged to phylotype I. Partial sequences of HrpB were identical among phylotype I strains except for one strain. Analyses using the partial nucleotide sequences of the gyrB and egl gene fragments grouped phylotype I strains into 11 gyrB and 8 egl types, respectively, whereas analyses using the partial amino acid sequences of GyrB and Egl grouped phylotype I strains into 4 GyrB and 5 Egl types, respectively. Using multilocus sequence typing of GyrB and Egl, we identified 10 unique sequence types within the Japanese phylotype I strains. Strains belonging to the GyrB42 or GyrB66 type caused wilt in tobacco, and strains belonging to GyrB2 or GyrB9 type elicited HR, demonstrating that HR induction in tobacco is genetically differentiated in the Japanese strains of R. solanacearum.     

黄土高原重力侵蚀的地质地貌因素分析--从发生的规模频度看区域特征

在按规模和频度对黄土高原重力侵蚀分类的基础上,分析了重力侵蚀具有普遍性、沿河谷分布、区域差异明显等区域分布特点。并分析了地质地貌因素对各种主要重力侵蚀形成与分布的影响:塌陷在碳酸盐地层存在地分布较多,高陡边坡地区易于形成巨大滑坡,群发性崩塌、滑坡以及泥流的形成多发生在沟谷密度较大地区,巨大泥流的形成在沟头地区多有较大的汇水面积等。因此在防治重力侵蚀过程中,必须充分地研究各地的地质地貌条件,因地制宜地防治不同类型的重力侵蚀。     

Characterization of a Phytophthora mating hormone

Water molds of the genus Phytophthora include many plant pathogens responsible for epidemics such as potato blight and sudden oak death, causing global economic damages. Sexual reproduction is of biological importance in Phytophthora and has been believed to be stimulated by unknown endogenous factors named a hormones. We describe here the chemical characterization of a Phytophthora mating hormone, a1, which was obtained from approximately 2 tons of culture fluid of one mating type of a species and which induced sexual spores on the counter-mating type at a nanogram level.