Molecular and genetical dissection ofthe mechanism underlying cytoplasmic male sterility in sugar beet

剖析编码线粒体基因的雄性不育基因(S)和抑制雄性不育的核基因(命名为Rf)的性质，对于理解甜菜细胞质雄性不育的机理具有重要意义。在此，我们试图克隆和鉴定控制甜菜不育系育性恢复的Rf1基因。研究结果如下：1.研究结果。我们能够将Rf1基因座的可能位置限制在至少6个BAC克隆，跨度约为260kb。260kb的核苷酸序列分析显示有28个ORFs。在28个ORF中，我们发现了4个ORF，它们在花蕾中特异表达，并定位于线粒体。这四个ORF彼此相邻，都是金属蛋白酶的代号。我们将ORF命名为MPLS。有趣的是，在一个不可恢复的(Rf1rf1)基因中，我们发现了同源ORF，这些ORF存在缺失，并且不在花蕾中表达。原位杂交分析表明，MPLS仅在小孢子四分体和幼孢子时期的花药绒毡层细胞中表达。综上所述，我们的观察结果强烈表明，MPLs。为了将线粒体损伤与不育花药的细胞代谢过程联系起来，我们发现了一个花药特异的脂转移蛋白基因(LTP)。该基因在可育花药的幼年小孢子阶段高表达，但在不育花药整个发育过程中不表达。这很可能是由于CMS细胞质引起的线粒体功能障碍和随后的生理变化，LTP在绒毛膜中的表达下调。

Dissecting the nature of male-sterility encoding mitochondrial gene(s) and the nuclear genes (named Rf) that suppress male sterility is quite instructive in understanding the mechanism of cytoplasmic male sterility (CMS) in sugar beet. Here we attempted to clone and characterize the Rf1 locus which controls fertility restoration in sugar beet CMS. The results are as follows.1. We were able to restrict the possible location of the Rf1 locus to a minimum of six BAC clones spanning an interval of about 260kb. The nucleotide sequencing of the 260-kb region revealed 28 ORFs.2. Among the 28 ORFs, we found four ORFs which are specifically expressed in flower buds and targeted to mitochondria.3. The four ORFs are adjacent to one another and all code for metalloprotease. We designated the ORFs MPLs. Interestingly, in a nonrestoring (rf1rf1) genotype we identified homologous ORFs that exhibit deletions and are not expressed in flower buds.4. In situ hybridization analysis demonstrated that expression of MPLs is confined to the tapetal cells of anthers at the microspore tetrad and young microspore stages. Taken together, our observations suggest strongly that MPLs5. In an attempt to correlate mitochondrial lesions with cellular metabolic processes in sterile anthers, we found an anther-specific lipid transfer protein gene (named LTP).The gene was revealed to be highly expressed in the tapetal cells of fertile anthers at the young microspore stage but not in sterile anthers throughout flower development. It is most likely that the expression of LTP is down-regulated in the tapetum in response to mitochondrial dysfunction and subsequent physiological changes caused by CMS cytoplasm.