Phosphate Concentration and Arbuscular Mycorrhizal Colonisation Influence the Growth, Yield and Expression of Twelve PHT1 Family Phosphate Transporters in Foxtail Millet (Setaria italica)

Phosphorus (P) is an essential element which plays several key roles in all living organisms. Setaria italica (foxtail millet) is a model species for panacoid grasses including several millet species widely grown in arid regions of Asia and Africa, and for the bioenergy crop switchgrass. The growth responses of S. italica to different levels of inorganic phosphate (Pi) and to colonisation with the arbuscular mycorrhizal fungus Funneliformis mosseae (syn. Glomus mosseae) were studied. Phosphate is taken up from the environment by the PHT1 family of plant phosphate transporters, which have been well characterized in several plant species. Bioinformatic analysis identified 12 members of the PHT1 gene family (SiPHT1;1-1;12) in S. italica, and RT and qPCR analysis showed that most of these transporters displayed specific expression patterns with respect to tissue, phosphate status and arbuscular mycorrhizal colonisation. SiPHT1;2 was found to be expressed in all tissues and in all growth conditions tested. In contrast, expression of SiPHT1;4 was induced in roots after 15 days growth in hydroponic medium of low Pi concentration. Expression of SiPHT1;8 and SiPHT1;9 in roots was selectively induced by colonisation with F. mosseae. SiPHT1;3 and SiPHT1;4 were found to be predominantly expressed in leaf and root tissues respectively. Several other transporters were expressed in shoots and leaves during growth in low Pi concentrations. This study will form the basis for the further characterization of these transporters, with the long term goal of improving the phosphate use efficiency of foxtail millet.

磷（Phosphorus, P）是所有活生物体的必需元素，在各类生命活动中发挥多重关键作用。谷子（Setaria italica，foxtail millet）是黍亚科禾草的模式物种，该类群涵盖多个在亚洲与非洲干旱地区广泛种植的粟类物种，以及能源作物柳枝稷（switchgrass）。本研究针对谷子对不同浓度无机磷酸盐（inorganic phosphate, Pi）的生长响应，以及其与丛枝菌根真菌摩西斗管囊霉（Funneliformis mosseae，异名Glomus mosseae）的共生定殖过程展开探究。植物可通过PHT1家族磷酸盐转运蛋白从环境中摄取磷酸盐，该蛋白家族已在多种植物中得到充分功能表征。通过生物信息学分析，本研究在谷子基因组中鉴定出PHT1基因家族的12个成员（SiPHT1;1至SiPHT1;12）；反转录PCR（RT）与实时定量PCR（qPCR）分析显示，多数转运蛋白的表达模式具有组织特异性、磷酸盐应答特异性以及对丛枝菌根定殖的响应特异性。其中，SiPHT1;2在所有检测的组织与生长条件下均有表达。与之相反，SiPHT1;4在低Pi浓度水培培养基中培养15天后的根组织中被诱导表达。SiPHT1;8与SiPHT1;9在根中的表达仅被摩西斗管囊霉的定殖所诱导。SiPHT1;3与SiPHT1;4分别主要在叶片与根组织中优势表达。另有多个转运蛋白在低Pi浓度培养条件下的地上组织与叶片中表达。本研究为这些磷酸盐转运蛋白的后续功能表征奠定了基础，最终长期目标是提升谷子的磷酸盐利用效率。