南湖新聞網(wǎng)訊 植物激素在植物生長(zhǎng)發(fā)育、抵抗生物和非生物脅迫中發(fā)揮著重要的調(diào)控作用。近日，華中農(nóng)業(yè)大學(xué)植物營(yíng)養(yǎng)生物學(xué)團(tuán)隊(duì)研究揭示了油菜素甾醇（BRs）和茉莉酸（JA）參與植物響應(yīng)缺硼脅迫的分子調(diào)控機(jī)制。

 

　　油菜素甾醇（brassinosteroids, BRs）是一類多羥基的甾醇類植物激素，因首先從油菜花粉中發(fā)現(xiàn)提取而得名，廣泛分布在植物的根、莖、葉片、花、種子和幼嫩的生長(zhǎng)組織中，調(diào)控植物的生長(zhǎng)發(fā)育。植物缺硼會(huì)嚴(yán)重抑制主根的生長(zhǎng)，該團(tuán)隊(duì)通過(guò)研究分析擬南芥響應(yīng)缺硼和BR的RNA-seq結(jié)果，發(fā)現(xiàn)兩者共表達(dá)的基因數(shù)高達(dá)45.9%（圖1c），且這些共表達(dá)的基因大部分呈現(xiàn)相反的表達(dá)趨勢(shì)。與野生型相比，BR的受體突變體bri1-119和bri1-301表現(xiàn)出對(duì)低硼脅迫不敏感，而B(niǎo)R信號(hào)增強(qiáng)突變體bes1-D對(duì)缺硼脅迫則表現(xiàn)出顯著高的抗性（圖1a）。此外，外源添加24-表油菜素內(nèi)酯（eBL）能顯著緩解根的生長(zhǎng)抑制（圖1b），而添加BR合成抑制劑BRZ會(huì)加重根生長(zhǎng)的抑制，且缺硼減少了BES1的核信號(hào)，但在缺硼條件下添加eBL則能增加BES1的核信號(hào)。進(jìn)一步研究發(fā)現(xiàn)缺硼通過(guò)抑制BR合成基因BR6ox1和BR6ox2的表達(dá)而減少了油菜素內(nèi)酯（BL）的合成（圖1d）。

 

　　茉莉酸（JA）是調(diào)節(jié)植物生長(zhǎng)發(fā)育、抵御逆境脅迫的一種植物激素。植物營(yíng)養(yǎng)生物學(xué)團(tuán)隊(duì)研究發(fā)現(xiàn)缺硼條件下擬南芥地上部和根中積累JA達(dá)到正常硼條件下的7.9倍和2.8倍，生長(zhǎng)受嚴(yán)重抑制，外源添加JA合成抑制劑DIECA則可以緩解缺硼對(duì)生長(zhǎng)的抑制。團(tuán)隊(duì)進(jìn)一步鑒定到一個(gè)缺硼誘導(dǎo)的乙烯轉(zhuǎn)錄因子ERF018，通過(guò)作用于JA合成基因AOCs的啟動(dòng)子區(qū)域，上調(diào)了JA合成基因的表達(dá)，使JA合成增多。在茉莉酸氨基酸結(jié)合酶JAR1的作用下，增多的JA進(jìn)一步轉(zhuǎn)變?yōu)橛猩锘钚孕问降能岳蛩?異亮氨酸JA-Ile。JA-Ile與受體復(fù)合物SCFCOI1結(jié)合激活JA下游信號(hào)，參與缺硼對(duì)擬南芥生長(zhǎng)的抑制。同時(shí)，研究發(fā)現(xiàn)缺硼上調(diào)了乙烯（ET）合成基因的表達(dá)，使ET積累，并負(fù)調(diào)主根生長(zhǎng)。JA通過(guò)抑制jar1-1突變體中乙烯信號(hào)轉(zhuǎn)錄因子EIN3的蛋白水平，從而實(shí)現(xiàn)JA與ET協(xié)同作用于缺硼對(duì)主根生長(zhǎng)的抑制。JA并不直接調(diào)控硼的吸收轉(zhuǎn)運(yùn)，而是通過(guò)影響缺硼時(shí)根系構(gòu)型而影響硼的吸收。

 

　　上述研究獲得了國(guó)家自然科學(xué)基金、國(guó)家重點(diǎn)研發(fā)計(jì)劃和中央高?；究蒲袠I(yè)務(wù)費(fèi)專項(xiàng)基金資助，團(tuán)隊(duì)成員汪社亮副研究員、王創(chuàng)研究員，丁廣大副教授，蔡紅梅副教授和石磊教授等參與了研究工作。

 

　　【英文摘要】

 

　　Brassinosteroids （BRs） are pivotal phytohormones involved in dominating root development. Boron （B） is an essential micronutrient for plants, and root growth is rapidly inhibited under B‐deficiency conditions. However, the mechanisms underlying this inhibition are still unclear. Here, we identified BR‐related processes underlying B deficiency at the physiological, genetic, molecular/cell biological and transcriptomic levels and found strong evidence that B deficiency can affect BR biosynthesis and signalling, thereby altering root growth. RNA sequencing analysis revealed strong co‐regulation between BR‐regulated genes and B deficiency‐responsive genes. We found that the BR receptor mutants bri1‐119 and bri1‐301 were more insensitive to decreased B supply, and the gain‐of function mutants bes1‐D and pBZR1‐bzr1‐D lines exhibited insensitivity to low‐B stress. Under B‐deficiency conditions, exogenous 24‐epibrassinolide （eBL） rescued the inhibition of root growth, and application of the BR biosynthesis inhibitor BRZ exacerbated this inhibitory effect. The nuclear‐localized signal of BES1 was reduced under low‐B conditions compared with B‐sufficiency conditions. We further found that B deficiency hindered the accumulation of brassinolide （BL） to downregulate BR signalling and modulate root elongation, which may occur through a reduction in BR6ox1 and BR6ox2 mRNA levels. Taken together, our results reveal a role of BR signalling in root elongation under B deficiency.

 

　　The essential micronutrient boron （B） has key roles in cell wall integrity and B deficiency inhibits plant growth. The role of jasmonic acid （JA） in plant growth inhibition under B deficiency remains unclear. Here, we report that low B elevates JA biosynthesis in Arabidopsis thaliana by inducing the expression of JA biosynthesis genes. Treatment with JA inhibited plant growth and, a JA biosynthesis inhibitor enhanced plant growth, indicating that the JA induced by B deficiency affects plant growth. Furthermore, examination of the JA signaling mutants jasmonate resistant1, coronatine insensitive1‐2, and myc2 showed that JA signaling negatively regulates plant growth under B deficiency. We identified a low‐B responsive transcription factor, ERF018, and used yeast one‐hybrid assays and transient activation assays in Nicotiana benthamiana leaf cells to demonstrate that ERF018 activates the expression of JA biosynthesis genes. ERF018 overexpression （OE） lines displayed stunted growth and up‐regulation of JA biosynthesis genes under normal B conditions, compared to Col‐0 and the difference between ERF018 OE lines and Col‐0 diminished under low B. These results suggest that ERF018 enhances JA biosynthesis and thus negatively regulates plant growth. Taken together, our results highlight the importance of JA in the effect of low B on plant growth.

 

　　論文鏈接：

 

　　https://onlinelibrary.wiley.com/doi/10.1111/tpj.15311

 

　　https://academic.oup.com/jxb/article/72/8/3108/6126775

 

　　https://onlinelibrary.wiley.com/doi/10.1111/jipb.13048