不同磷效率基因型小麦应对缺磷胁迫的表型及相关基因表达的研究

Time-course response of phenotype and the expression of Pi-starvation responsive genes in high and low Pi-efficient wheat genotypes to Pi starvation

【目的】小麦是磷肥需求量最大的作物之一。为了探索小麦对磷的高效利用机制,本研究评价了不同磷效率基因型小麦在缺磷条件下的差异响应。【方法】本研究选取一个磷高效小麦基因型‘小偃54’和一个低效率型‘中国春’作为试验材料,设置正常供磷(+P)、缺磷(−P)和缺磷7天后恢复正常供磷(RP)3个处理进行小麦水培试验,调查分析了小麦幼苗的表型、生理以及缺磷响应基因的表达随缺磷时间的变化趋势,及它们在不同磷效率小麦基因型间的异同。【结果】缺磷胁迫明显增加了两个小麦基因型的根冠比,但无论缺磷与否,磷高效基因型‘小偃54’的根冠比均大于磷低效基因型‘中国春’。随着缺磷时间的延长,小麦幼苗地上、地下部无机磷和总磷浓度逐渐降低,但不同基因型之间无明显差异。对缺磷的小麦幼苗恢复供磷后,磷耗竭的小麦幼苗体内无机磷含量迅速增加,‘小偃54’地上、地下部的无机磷含量均明显高于‘中国春’。缺磷响应信号基因TaIPS1和TaSPX3在缺磷6 h即被诱导表达,随着缺磷时间的延长表达量逐渐升高,且恢复供磷后表达量显著降低;缺磷早期‘中国春’中TaIPS1和TaSPX3的表达量比小偃54高,但在长期缺磷和缺磷后恢复供磷处理下又比‘小偃54’低,表明磷低效小麦基因型‘中国春’可能对体内磷稳态变化更为敏感。然而,两个根系特异表达的高亲和磷转运子TaPHT1.1/9和TaPHT1.10均表现出缺磷早期表达受到抑制,而长期缺磷被诱导升高表达。未预料到的是,二者在复磷处理后的表达量明显高于缺磷处理。长期缺磷处理下,‘中国春’中TaPHT1.1/9的表达量明显低于‘小偃54’,但其TaPHT1.10的表达与‘小偃54’无显著差异,表明不同磷效率基因型小麦幼苗缺磷诱导表达的磷吸收转运子可能存在差异。除此以外,缺磷胁迫显著增加了‘中国春’根系DCB-Fe含量,但对‘小偃54’无明显影响。【结论】磷高效基因型小麦幼苗(‘小偃54’)比磷低效型(‘中国春’)具有更大的根冠比和更强的磷吸收能力。‘小偃54’根系中的磷转运子基因TaPHT1.1/9的表达也明显高于‘中国春’。然而,缺磷明显促进了磷低效基因型小麦根表铁的富集。今后将进一步研究小麦根表铁的富集对小麦幼苗磷高效吸收和利用的影响。

【Objectives】Phosphate(Pi)deficiency affects the growth and production of wheat.Many contrasting Pi-efficient wheat genotypes have been developed for improving yield in low-Pi soils.They are also important to sustainable agricultural systems.This study compares the response of seedlings of high and low Piefficient wheat cultivars to Pi deficiency.【Methods】A high Pi-efficient wheat genotype‘Xiaoyan 54’(XY)and a low Pi-efficient genotype‘Chinese Spring’(CS),were selected for a hydroponic experiment.The treatments were sufficient Pi(+P),Pi deficiency(−P),and the resupply of Pi after its deprivation(RP).The time-course response of the wheat seedlings to Pi deficiency was analyzed at morphological and physiological levels.Further,the expression of Pi-starvation responsive genes in wheat seedlings of the two contrasting Pi-efficient genotypes was recorded.【Results】The shoot biomass in XY was lower than in CS,while the root biomass showed no significant difference between the two genotypes regardless of Pi supply.Correspondingly,the root-shoot ratio in XY was higher than in CS.Although Pi and total P concentrations in the roots and shoots of wheat seedlings gradually decreased with Pi starvation,no significant difference was observed between the two genotypes.When Pi was resupplied,its concentration in the Pi-starved seedlings immediately increased.The Pi concentration in the roots and shoots of XY was higher than in CS.TaIPS1 and TaSPX3-the sensors to Pi-starvation response in plants-were highly induced at the transcriptional level in tandem with the reduction of Pi concentration in the plants.However,the expression of these genes declined when Pi was resupplied in the Pi-starved seedlings.At the early stage of Pi starvation,the expression of these genes in CS was higher than in XY.This was reversed due to long-term Pi depletion,suggesting that the low Pi-efficient genotype was more sensitive to Pi starvation.In contrast,the expression levels of TaPHT1.1/9 and TaPHT1.10 were inhibited at the initial stage of Pi deprivation but highly induced under long-term Pi starvation.The resupply of Pi more highly induced the expression levels of two TaPHT1 genes than Pi sufficient and deficient treatments.Concerning the two different genotypes,the expression of TaPHT1.1/9 was(P<0.05)higher in XY than CS in the long-term Pi starvation treatment,while the transcripts of TaPHT1.10 showed no significant(P>0.05)difference between them.In addition,Pi starvation(P<0.05)accelerated the Fe accumulation on the root surface of CS but showed a minimal effect on XY.【Conclusions】The high Pi-efficient genotype(XY)had a larger root-shoot ratio and stronger Pi uptake.In contrast,the low Pi-efficient genotype(CS)accumulated more Fe on the root surface under Pi starvation.Therefore,it is valuable to explore further how Fe accumulation on the root surface affects the efficiency of uptake and utilization of Pi.