柑橘不同砧穗组合对硼吸收与转运效率差异的机制研究

The interaction between rootstock and scion of fruit trees affect plant growth. Most information about rootstocks affect scion have been reported. However, relatively few reports were about scion affect growth and nutrient uptake of rootstock. Previous studies show that there are significant differences about growth and boron uptake and translocation efficiency of the same trifoliate orange rootstock for very close genetic relationship of different citrus varieties, the molecular mechanisms underlying the process are unclear to date. The project plans to using boron deficiency sensitive of two rootstocks and two scion citrus varieties grafted to the formation of four rootstock-scion combinations under boron deficiency condition. In order to understand the difference of boron uptake and transport for each rootstock-scion combination, boron content of rootstock and scion was determined. Furthermore, to relationship between boron absorption and translocation of IAA levels, IAA and other hormones in the dynamic among the different rootstock-scion combinations were also determined. Combination of roots and stems and leaves of the scion at the transcriptional level expression differences to identify involved in boron uptake and operation of closely related genes and their metabolic pathways under boron deficiency. In addition, the differences of miRNA expression was studied high throughput sequencing technology, these results indicates that sieve tube has an important role in the absorption and transport of the roots of boron. This will not only advance the citrus scion interaction mechanisms, but also provide a theoretical basis to solve the nutrient imbalances between rootstock and scion.

果树通过砧木和接穗间的互作影响植株生长。砧木对地上部接穗的影响不言而喻，但接穗对砧木根系生长和养分吸收的研究却鲜见报道。前期研究表明，亲缘关系极近的不同柑橘品种，对同一枳砧的生长及硼的吸收和转运效率存在着显著差异，其机制尚不清楚。本项目拟以对缺硼敏感差异较大的2个砧木和2个接穗品种为材料，嫁接形成两两组合并进行缺硼处理：测定砧穗各部位硼等元素的含量，以明确各砧穗组合对硼的吸收与转运的差异；测定IAA等激素在不同砧穗间的动态，以明确接穗影响根系的IAA水平及与硼吸收运转的关系；在转录水平上比较不同砧穗组合的根系和茎叶在缺硼胁迫下的表达差异，找出参与硼吸收和运转密切相关的基因及其代谢途径。此外，通过高通量测序技术调查砧穗之间miRNA表达的差异，探讨其通过筛管的转运对根部硼吸收和转运的作用。这不但可将柑橘砧穗互作机制研究推向前进，还可为解决砧穗养分失衡问题提供理论依据。

本研究以对缺硼敏感差异明显的柑橘砧木和品种为材料，互为嫁接形成纽荷尔脐橙/枳、纽荷尔/枳橙、奉节脐橙/枳、奉节脐橙/枳橙等不同的砧穗组合。分别从生理、转录和转录后水平对四种砧穗组合在缺硼条件下硼吸收与转运的差异进行了研究。结果表明：.（1）生理水平研究：在缺硼条件下，奉节脐橙芽和叶的硼含量显著高于纽荷尔，叶片硼分配率较纽荷尔下降少，根却相反；纽荷尔/枳橙接穗茎的硼分配率高于其他组合；枳橙砧组合叶片的可利用态硼比例显著高于枳砧组合；以奉节脐橙为接穗的组合，根的可利用态硼比例显著高于纽荷尔的；枳橙的叶片硼临界浓度显著低于枳的。.（2）柑橘品种对砧木缺硼耐受性转录测序研究：在1931个差异表达基因中，以奉节脐橙为接穗的组合，其根的水通道蛋白基因、细胞壁合成和伸展相关基因的表达均高于纽荷尔，木质素合成关键酶基因的表达均低于纽荷尔，说明奉节脐橙为接穗有较强耐缺硼能力。.（3）柑橘砧木对接穗缺硼耐受性转录测序研究：在1900个差异表达基因中，以枳橙为砧木的组合，叶片光合作用、叶绿素降解、葡萄糖及果糖合成相关的基因的变幅均低于枳砧的；同时生长素运输和响应、脱酸酸合成等相关基因的变幅，也均低于枳砧纽荷尔的。从而说明枳橙砧组合对缺硼有着较强的耐受性。.（4）不同柑橘砧穗组合缺硼耐受性miRNA表达分析：缺硼胁迫下调控抗氧化酶活性相关miRNA下调表达，调控根系发育相关miRNA上调表达，调控植株生长miRNA下调表达。奉节脐橙根miRNA变化程度高于纽荷尔，枳橙砧纽荷尔叶片miRNA变化程度高于枳砧纽荷尔。因此，枳橙作为砧木、奉节脐橙作为接穗对缺硼有着较强的耐受性。.（5）缺硼胁迫基本不影响根尖细胞周期相关基因的表达，而显著影响了根尖伸长相关基因的表达，从而导致根尖逐渐膨大坏死。同时枳根中IAA的含量与其合成相关基因的变化一致；同时向基性转运蛋白基因显著下调表达，而向顶性转运蛋白基因上调表达。