Dipartimento di OrtoFloroArboricoltura e Tecnologie Agroalimentari, University of Catania, Via Valdisavoia 5, Catania, 95123, Italy.
Plant Cell Rep. 2009 Sep;28(9):1439-51. doi: 10.1007/s00299-009-0744-9. Epub 2009 Jul 28.
In contrast to model species, the self-incompatibility reaction in citrus has been poorly studied. It is assumed to be gametophytically determined and genetically controlled by the S-locus, which in other species encodes for glycoproteins (S-RNases) showing ribonuclease activity. To investigate pollen-pistil interaction, the pollen tube growth of two clementine varieties, 'Comune' (self-incompatible) and 'Monreal' (a 'Comune' self-compatible mutation) was analysed by histological assays in self- and cross-pollination conditions. Cross-pollination assays demonstrated that the mutation leading to self-compatibility in 'Monreal' occurred in the stylar tissues. Similar rates of pollen germination were observed in both genotypes. However, 'Comune' pollen tubes showed altered morphology and arrested growth in the upper style while in 'Monreal' they grew straight toward the ovary. Moreover, to identify genes putatively involved in pollen-pistil interaction and self-incompatibility, research based on the complementary DNA-amplified fragment length polymorphism technique was carried out to compare the transcript profiles of unpollinated and self-pollinated styles and stigmas of the two cultivars. This analysis identified 96 unigenes such as receptor-like kinases, stress-induced genes, transcripts involved in the phenylpropanoid pathway, transcription factors and genes related to calcium and hormone signalling. Surprisingly, a high percentage of active long terminal repeat (LTR) and non-LTR retrotransposons were identified among the unigenes, indicating their activation in response to pollination and their possible role in the regulation of self-incompatibility genes. The quantitative reverse trascription-polymerase chain reaction analysis of selected gene tags showed transcriptional differences between the two genotypes during pollen germination and pollen tube elongation.
与模式物种相比，柑橘的自交不亲和反应研究甚少。据推测，它是配子体决定的，由 S 基因座遗传控制，该基因座在其他物种中编码具有核糖核酸酶活性的糖蛋白（S-RNases）。为了研究花粉-雌蕊相互作用，通过组织学分析，研究了两个克莱门氏小柑橘品种“Comune”（自交不亲和）和“Monreal”（“Comune”自交亲和突变）在自交和杂交授粉条件下的花粉管生长。杂交授粉试验表明，导致“Monreal”自交亲和的突变发生在花柱组织中。在两种基因型中观察到相似的花粉萌发率。然而，“Comune”花粉管在上部花柱中表现出形态改变和生长停滞，而在“Monreal”中它们则笔直地向子房生长。此外，为了鉴定可能参与花粉-雌蕊相互作用和自交不亲和的基因，基于 cDNA 扩增片段长度多态性技术的研究用于比较两个品种未授粉和自授粉花柱和柱头的转录谱。该分析鉴定了 96 个单基因，如受体样激酶、应激诱导基因、参与苯丙烷途径的转录本、转录因子和与钙和激素信号相关的基因。令人惊讶的是，在单基因中鉴定出了大量活跃的长末端重复（LTR）和非 LTR 反转录转座子，表明它们在授粉后被激活，可能在自交不亲和基因的调控中发挥作用。对选定基因标签的定量逆转录-聚合酶链反应分析显示，在花粉萌发和花粉管伸长过程中，两种基因型之间存在转录差异。
