Nucleo-cytoplasmic interactions affect RNA editing of cox2, atp6 and atp9 in alloplasmic male-sterile rice (Oryza sativa L.) lines

RNA editing plays an important role in the regulation of mitochondrial gene expression in flowering plants. In this study, we examined RNA editing of the mitochondrial genes cox2, atp6 and atp9 in five isonuclear alloplasmic male-sterile lines (IAMSLs) of rice to investigate whether different cytoplasmic types affect RNA editing. Although many editing sites were conserved among the three genes, we found that the editing efficiency of certain sites was significantly different between different IAMSLs or between IAMSLs and their corresponding cytoplasmic donor CMS lines. Furthermore, several editing sites were found to be either present or absent in certain IAMSLs and their corresponding CMS lines. These results indicate that nuclear loci, as well as unknown editing factors within the mitochondria of different cytoplasmic types, may be involved in RNA editing, and they suggest that RNA editing in plant mitochondria is affected by nucleo-cytoplasmic interactions.     

Analysis of genetic diversity in cytoplasmic male sterility,and association of mitochondrial genes with petaloid-type cytoplasmic male sterility in tuber mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis> var. <Emphasis Type="Italic">tumida</Emphasis> Tsen et Lee)

In our previous study, we bred a stable cytoplasmic male sterility (CMS) line of tuber mustard by using distant hybridization and subsequent backcrosses. In this CMS plants, all floral organs are normal except the anthers, which are transformed into petals or tubular structures. Recently, 2 mitochondrial genes—atpA and orf220—that are distinctively present in the CMS line of tuber mustard were cloned and partially characterized. In our study of genetic diversity analysis of CMS, 7 species of Brassica and Raphanus crops, which included 5 CMS lines and their respective maintainer lines, were used to compare the constitution of protein-coding genes in the mitochondrial genomes. In 4 of the 43 mitochondrial genes, namely, atpA, orf220, orf256, and orf305/orf324, polymorphisms were detected among the tuber mustard CMS line and its maintainer line. The results of a cluster analysis indicate that petaloid CMS phenotype of tuber mustard is a novel CMS type and is nearer to the nap CMS in Brassica napus at the phylogenetic level. The results of individual amplifications of these genes indicate the presence of 4 sequence-characterized amplified region (SCAR) markers, which enable rapid and reliable identification of this CMS. Expressions of the orf220 and orf256 genes were detected only in the CMS line, while expression of the orf305 gene was detected in the maintainer line. The different expression patterns of different mitochondrial-specific marker genes indicate that the quantity of mitochondrial proteins is differentially regulated during organ/tissue development in tuber mustard. The results of this study suggest that the above mentioned 4 mitochondrial genes are associated with the petaloid CMS phenotype in tuber mustard.     

Heterotopic expression of class B floral homeotic genes supports a modified ABC model for tulip (Tulipa gesneriana)

In higher eudicotyledonous angiosperms the floral organs are typically arranged in four different whorls, containing sepals, petals, stamens and carpels. According to the ABC model, the identity of these organs is specified by floral homeotic genes of class A, A+B, B+C and C, respectively. In contrast to the sepal and petal whorls of eudicots, the perianths of many plants from the Liliaceae family have two outer whorls of almost identical petaloid organs, called tepals. To explain the Liliaceae flower morphology, van Tunen et al. (1993) proposed a modified ABC model, exemplified with tulip. According to this model, class B genes are not only expressed in whorls 2 and 3, but also in whorl 1. Thus the organs of both whorls 1 and 2 express class A plus class B genes and, therefore, get the same petaloid identity. To test this modified ABC model we have cloned and characterized putative class B genes from tulip. Two DEF- and one GLO-like gene were identified, named TGDEFA, TGDEFB and TGGLO. Northern hybridization analysis showed that all of these genes are expressed in whorls 1, 2 and 3 (outer and inner tepals and stamens), thus corroborating the modified ABC model. In addition, these experiments demonstrated that TGGLO is also weakly expressed in carpels, leaves, stems and bracts. Gel retardation assays revealed that TGGLO alone binds to DNA as a homodimer. In contrast, TGDEFA and TGDEFB cannot homodimerize, but make heterodimers with PI. Homodimerization of GLO-like protein has also been reported for lily, suggesting that this phenomenon is conserved within Liliaceae plants or even monocot species.these authors contributed equally to this work     

Genetic variation of petaloid male-sterile cytoplasm of carrots revealed by sequence-tagged sites (STSs)

The mitochondrial DNA of various carrot lines was characterized by random amplified polymorphic DNA (RAPD) analysis, and six sequence-tagged sites (STSs) led to identification of the petaloid type of cytoplasmic male sterility (CMS). Using six STS primer combinations, we were able to classify five CMS lines into two groups and eight fertile carrots into six groups. Both the STS1 and the STS4 primer combinations differentiated CMS cytoplasms from the fertile cytoplasms, and the STS2 primer combination revealed two different types of CMS cytoplasms – of Wisconsin Wild and Cornell origins. Cybrid carrot lines with petaloid flowers which had been obtained by asymmetric cell fusion could also be separated from fertile cybrids by the STS1 primer combination. The STS1 fragment contained a homologous sequence with the orfB gene. DNA gel blot analysis indicated that homologous regions to the STS1 fragment existed in fertile types as well as the CMS types, although the restriction fragment size patterns differed. These observations demonstrate that rearrangements involving this region occurred in the mitochondrial genome. The STS4 fragment had a more complicated gene structure, including retrotransposon-like sequences and small segments of chloroplast genome. Received: 10 September 1998 / Accepted: 24 February 1999     

植物细胞质雄性不育与线粒体

细胞质雄性不育(cytoplasmic male sterility, CMS)是由于核基因组与细胞质基因组之间不协调互作导致的一种雄性器官异常而雌器官可以接受外来花粉正常结实的自然现象。在生产上,CMS是植物杂交制种的有力工具和杂种优势利用的重要途径。对CMS分子机制的解析是其有效利用的基础,一直以来都是研究的热点,然而其机制研究却相对滞后。该文从线粒体嵌合基因(orfs)形成、特征及分类,基因转录后修饰(RNA编辑)的特点及与CMS的关系,基因翻译产物特征、分类及其与CMS的关系等3个方面综述了近年来植物胞质雄性不育的机制研究进展,以期为进一步深入解析其分子机制提供理论参考。     

Plant development going MADS

It has been known for a decade that the plant MADS genesare important regulators of meristem and floral organ identity. The MADS family in Arabidopsis consists of more than 80 members and, until recently, the function of the majority of these genes was unknown. With the enhanced ability to generate loss-of-function mutants and over-expression lines, the function of the MADS gene family members is beginning to be elucidated. Recent progress demonstrates that MADS genes in Arabidopsis are important regulators not only of meristem and floral organ identity but also of flowering timing and cell-type specification in floral organs.