低植酸作物遗传改良途径与磷资源高效利用

  【目的】  磷是作物生长发育所必需的营养元素。在植物体内，磷多以植酸形式储存在成熟籽粒中。非反刍动物，包括人类，无法消化植酸来获取磷及植酸螯合的有益元素，籽粒中收获的大量磷素进入人及动物排泄物，不仅造成磷资源浪费，也加大了环境风险。因此，培育籽粒低植酸品种是改善作物营养品质、降低磷素环境风险的重要途径。本文综述作物籽粒磷的来源，控制籽粒植酸磷含量的主要生理过程及遗传改良策略等研究进展，为相关领域研究奠定基础。  主要进展  籽粒植酸磷的积累主要由3步组成，木质部或韧皮部向籽粒转运无机磷酸盐，籽粒利用无机磷酸盐合成植酸，植酸被运输至液泡中储存。目前已分离鉴定到负责相关过程的转运蛋白和关键酶及其编码基因，如SULTR3;4、SULTR3;3、PHT1;4蛋白介导无机磷酸盐向籽粒的转运，MIPS、ITPK、IPK1酶参与植酸的合成，以及MRP蛋白介导植酸合成后的转运储藏。对籽粒低植酸突变体的产量、农艺性状表型及改良策略的优缺点进行比较，籽粒低植酸品种可能存在产量下降、种子萌发率低等不足。  展望  未来可以从特异性修饰籽粒中关键基因的时空表达、发掘关键基因的优良等位变异及针对品种的磷营养管理3个方向，深入研发籽粒低植酸含量的高产品种，实现磷资源高效利用。

Genetic approaches to lower grain phytic acid for high phosphorus use efficiency in crops

  【Objectives】  Phosphorus (P) is an essential nutrient element for crop growth and development. In plants, P is mostly stored in mature grains in the form of phytic acid. Non ruminants, including humans, cannot digest phytic acid to utilize P and other nutrient elements owing to their chelation with phytic acid. This leads to decreased nutrition value and increased loss risk of P resources to environments via grain harvest and animal manure. Reducing grain phytic acid content is thus an important focus in crop breeding. We summarized the research progresses on pathway of P entering crop grains, the physiological processes regulating grain phytate-P, and genetic improvement strategies reducing grain phytate.   Main advances  The accumulation of phytate-P in grain was mainly composed of three steps: transporting inorganic P (Pi) from xylem or phloem and subsequently to grains, synthesizing phytic acid from Pi, and loading phytic acid into vacuole for storage. To date, many membrane transporters and metabolic enzymes involved in these processes have been characterized, such as SULTR3;4, SULTR3;3, PHT1;4 transporters mediating inorganic P transport to grains; MIPS, ITPK, IPK1 enzymes respond to phytic acid synthesis; and MRP proteins for vacuolar storage of phytic acid. We further compared yield performances and other agronomic traits of grain phytate mutants, and evaluated the different strategies of genetic improvements. The shortcoming of low grain phytate mutants remained, such as defective in yields formation and seeds germination rate.   Prospects  In the future, three approaches can be emphasized for breeding low-grain-phytate crop varieties, including modulating spatial-temporal expression of key genes, exploring superior gene allelic variation, and cultivars-specialized P nutrition management.