Iron (Fe) deficiency limits the yield of fruit trees. When subjected to Fe-deficiency, H+ secretion increases in the rhizosphere of dicotyledonous plants and pH decreases. This leads to the acidification of the soil and promotes Fe3+ to Fe2+ conversion, which plants can better uptake. This study investigated the relationship between two inhibitory transcription factors (ethylene response factors MbERF4 and MbERF72) and the H+-ATPase gene MbHA2. Two species of apple woody plants were studied: the Fe-inefficient Malus baccata and the Fe-efficient Malus xiaojinensis. Yeast one-hybrid and electrophoretic mobility shift assays showed that both MbERF4 and MbERF72 bind to the GCC cassette (AGCCGCC) of the MbHA2 promoter. Moreover, yeast two-hybrid and bimolecular fluorescence complementation assays showed that MbERF4 interacts with MbERF72. Furthermore, β-glucuronidase and luciferase reporter assays showed that the MbERF4- and MbERF72-induced repression of MbHA2 expression is synergistic. Virus-induced gene silencing of MbERF4 or MbERF72 increased MbHA2 expression, and thus lowered the rhizosphere pH in M. baccata. Consequently, the high expressions of MbERF4 and MbERF72 induced by Fe-deficiency contributed to the Fe sensitivity of M. baccata. Moreover, the low expressions of MxERF4 and MxERF72 contributed to the Fe-deficiency tolerance of M. xiaojinensis via different binding conditions to the HA2 promoter. In summary, this study identified the relationship of two inhibitory transcription factors with the H+-ATPase gene and proposed a model in which ERF4 and ERF72 affect the rhizosphere pH in response to Fe-deficiency.

中文翻译：

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乙烯响应因子MbERF4和MbERF72通过调节根际pH来抑制木本苹果植物中铁的吸收。

铁（Fe）缺乏限制了果树的产量。缺铁时，双子叶植物根际中的H +分泌增加，pH降低。这导致土壤酸化并促进Fe3 +向Fe2 +的转化，植物可以更好地吸收。这项研究调查了两个抑制转录因子（乙烯反应因子MbERF4和MbERF72）与H + -ATPase基因MbHA2之间的关系。研究了两种苹果木本植物：低铁低效海棠和低铁低效海棠。酵母一杂交和电泳迁移率变动分析表明MbERF4和MbERF72都与MbHA2启动子的GCC盒（AGCCGCC）结合。此外，酵母双杂交和双分子荧光互补测定法表明MbERF4与MbERF72相互作用。此外，β-葡萄糖醛酸苷酶和荧光素酶报告基因检测表明，MbERF4-和MbERF72诱导的MbHA2表达抑制是协同的。病毒诱导的MbERF4或MbERF72的基因沉默增加了MbHA2的表达，从而降低了巴卡德甲烷杆菌的根际pH。因此，铁缺乏引起的MbERF4和MbERF72的高表达有助于baccata烟草对Fe的敏感性。此外，MxERF4和MxERF72的低表达通过与HA2启动子的不同结合条件导致了小金娘对铁缺乏的耐受性。总之，这项研究确定了两个抑制转录因子与H + -ATPase基因的关系，并提出了一个模型，其中ERF4和ERF72响应铁缺乏而影响根际pH。