低植酸(肌醇-1,2,3,4,5,6-六磷酸(InsP6))作物的产生是重要的育种方向,但是这样的植物通常表现出不太理想的农艺性状。在这项研究中,通过甲磺酸乙酯介导的诱变,我们发现肌醇1,3,4-三磷酸5/6-激酶4(ITPK4),对于生产InsP6至关重要,是拟南芥耐盐性的关键调节剂。ITPK4基因的功能缺失导致盐胁迫下根伸长降低,这主要是因为根分生组织长度减少和分生组织细胞数量减少。itpk4突变还导致盐暴露期间根毛密度增加和活性氧积累增加。RNA测序分析显示,与野生型相比,itpk4-1突变体中的几种生长素响应基因下调。始终如一,itpk4-1突变体根尖的生长素水平降低,重力反应受损,表明ITPK4参与生长素信号通路的调节。通过抑制器筛选,发现多药耐药蛋白5(MRP5)5基因突变,它编码将InsP6从细胞质转运到液泡所需的ATP结合盒(ABC)转运蛋白,完全挽救了itpk4-1突变体的盐超敏反应,但是在itpk4-1mrp5双突变体中,InsP6保持在非常低的水平。这些结果暗示InsP6稳态而不是其总量对于植物的胁迫耐受性是有益的。总的来说,这项研究发现了一对基因突变,赋予低InsP6含量而不影响胁迫耐受性,这为创造“低植酸”作物提供了新的策略。
Generation of crops with low phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphosphate (InsP6)) is an important breeding direction, but such plants often display less desirable agronomic traits. In this study, through ethyl methanesulfonate-mediated mutagenesis, we found that inositol 1,3,4-trisphosphate 5/6-kinase 4 (ITPK4), which is essential for producing InsP6, is a critical regulator of salt tolerance in Arabidopsis. Loss of function of ITPK4 gene leads to reduced root elongation under salt stress, which is primarily because of decreased root meristem length and reduced meristematic cell number. The itpk4 mutation also results in increased root hair density and increased accumulation of reactive oxygen species during salt exposure. RNA sequencing assay reveals that several auxin-responsive genes are down-regulated in the itpk4-1 mutant compared to the wild-type. Consistently, the itpk4-1 mutant exhibits a reduced auxin level in the root tip and displays compromised gravity response, indicating that ITPK4 is involved in the regulation of the auxin signaling pathway. Through suppressor screening, it was found that mutation of Multidrug Resistance Protein 5 (MRP5)5 gene, which encodes an ATP-binding cassette (ABC) transporter required for transporting InsP6 from the cytoplasm into the vacuole, fully rescues the salt hypersensitivity of the itpk4-1 mutant, but in the itpk4-1 mrp5 double mutant, InsP6 remains at a very low level. These results imply that InsP6 homeostasis rather than its overall amount is beneficial for stress tolerance in plants. Collectively, this study uncovers a pair of gene mutations that confer low InsP6 content without impacting stress tolerance, which offers a new strategy for creating \"low-phytate\" crops.