Departamento de Bioquímica, Facultad de Química, Universidad Nacional Autónoma de México, Mexico City DF 04510, Mexico.
Plant Physiol. 2013 Jan;161(1):97-107. doi: 10.1104/pp.112.198440. Epub 2012 Nov 13.
In Solanaceae, the self-incompatibility S-RNase and S-locus F-box interactions define self-pollen recognition and rejection in an S-specific manner. This interaction triggers a cascade of events involving other gene products unlinked to the S-locus that are crucial to the self-incompatibility response. To date, two essential pistil-modifier genes, 120K and High Top-Band (HT-B), have been identified in Nicotiana species. However, biochemistry and genetics indicate that additional modifier genes are required. We recently reported a Kunitz-type proteinase inhibitor, named NaStEP (for Nicotiana alata Stigma-Expressed Protein), that is highly expressed in the stigmas of self-incompatible Nicotiana species. Here, we report the proteinase inhibitor activity of NaStEP. NaStEP is taken up by both compatible and incompatible pollen tubes, but its suppression in Nicotiana spp. transgenic plants disrupts S-specific pollen rejection; therefore, NaStEP is a novel pistil-modifier gene. Furthermore, HT-B levels within the pollen tubes are reduced when NaStEP-suppressed pistils are pollinated with either compatible or incompatible pollen. In wild-type self-incompatible N. alata, in contrast, HT-B degradation occurs preferentially in compatible pollinations. Taken together, these data show that the presence of NaStEP is required for the stability of HT-B inside pollen tubes during the rejection response, but the underlying mechanism is currently unknown.
在茄科植物中，自交不亲和 S-RNase 和 S 座位 F-box 的相互作用以 S 特异性的方式定义了自花粉的识别和排斥。这种相互作用触发了一系列涉及与 S 座位不连锁的其他基因产物的级联事件，这些基因产物对自交不亲和反应至关重要。迄今为止，已在烟草属物种中鉴定出两个必需的柱头修饰基因，120K 和 High Top-Band（HT-B）。然而，生物化学和遗传学表明需要其他修饰基因。我们最近报道了一种 Kunitz 型蛋白酶抑制剂，命名为 NaStEP（来自 Nicotiana alata 柱头表达蛋白），它在自交不亲和的烟草属物种的柱头上高度表达。在这里，我们报告了 NaStEP 的蛋白酶抑制剂活性。NaStEP 被亲和和不亲和花粉管吸收，但在烟草属转基因植物中的抑制破坏了 S 特异性花粉排斥；因此，NaStEP 是一个新的柱头修饰基因。此外，当用亲和或不亲和花粉授粉抑制 NaStEP 的柱头时，花粉管内的 HT-B 水平降低。相比之下，在野生型自交不亲和的 N. alata 中，HT-B 的降解优先发生在亲和授粉中。综上所述，这些数据表明，在排斥反应过程中，NaStEP 的存在是花粉管内 HT-B 稳定性所必需的，但目前尚不清楚其潜在机制。
