School of Sciences, University of Louisiana at Monroe, LA 71209, USA; Department of Genetics, University of Georgia, Athens, GA 30602, USA.
Department of Genetics, University of Georgia, Athens, GA 30602, USA.
Microbiol Res. 2024 Apr;281:127630. doi: 10.1016/j.micres.2024.127630. Epub 2024 Jan 28.
Iron (Fe) deficiency is a common mineral stress in plants, including sorghum. Although the soil fungus Trichoderma harzianum has been shown to mitigate Fe deficiency in some circumstances, neither the range nor mechanism(s) of this process are well understood. In this study, high pH-induced Fe deficiency in sorghum cultivated in pots with natural field soil exhibited a significant decrease in biomass, photosynthetic rate, transpiration rate, stomatal conductance, water use efficiency, and Fe-uptake in both the root and shoot. However, the establishment of T. harzianum colonization in roots of Fe-deprived sorghum showed significant improvements in morpho-physiological traits, Fe levels, and redox status. Molecular detection of the fungal ThAOX1 (L-aminoacid oxidase) gene showed the highest colonization of T. harzianum in the root tips of Fe-deficient sorghum, a location thus targeted for further analysis. Expression studies by RNA-seq and qPCR in sorghum root tips revealed a significant upregulation of several genes associated with Fe uptake (SbTOM2), auxin synthesis (SbSAURX15), nicotianamine synthase 3 (SbNAS3), and a phytosiderophore transporter (SbYS1). Also induced was the siderophore synthesis gene (ThSIT1) in T. harzianum, a result supported by biochemical evidence for elevated siderophore and IAA (indole acetic acid) levels in roots. Given the high affinity of fungal siderophore to chelate insoluble Fe ions, it is likely that elevated siderophore released by T. harzianum led to Fe(III)-siderophore complexes in the rhizosphere that were then transported into roots by the induced SbYS1 (yellow-stripe 1) transporter. In addition, the observed induction of several plant peroxidase genes and ABA (abscisic acid) under Fe deficiency after inoculation with T. harzianum may have helped induce tolerance to Fe-deficiency-induced oxidative stress and adaptive responses. This is the first mechanistic explanation for T. harzianum's role in helping alleviate Fe deficiency in sorghum and suggests that biofertilizers using T. harzianum will improve Fe availability to crops in high pH environments.
缺铁是植物中一种常见的矿物质胁迫，包括高粱。虽然土壤真菌哈茨木霉已被证明在某些情况下可以减轻铁缺乏症，但该过程的范围和机制尚不清楚。在这项研究中，在含有天然田间土壤的盆中种植的高粱，由于高 pH 值导致的铁缺乏症会导致生物量、光合速率、蒸腾速率、气孔导度、水分利用效率和根和地上部分的铁吸收显著下降。然而，在缺铁高粱的根部建立哈茨木霉的定植显示出在形态生理特性、铁水平和氧化还原状态方面的显著改善。真菌 ThAOX1（L-氨基酸氧化酶）基因的分子检测显示，在缺铁高粱的根尖处哈茨木霉的定植最高，因此该部位是进一步分析的目标。高粱根尖的 RNA-seq 和 qPCR 表达研究表明，与铁吸收相关的几个基因（SbTOM2）、生长素合成（SbSAURX15）、尼克酸胺合酶 3（SbNAS3）和植物螯合肽转运蛋白（SbYS1）的表达显著上调。哈茨木霉的铁载体合成基因（ThSIT1）也被诱导，这一结果得到了根系中铁载体和吲哚乙酸（IAA）水平升高的生化证据的支持。鉴于真菌铁载体与不溶性铁离子的高亲和力，哈茨木霉释放的高浓度铁载体很可能导致根际中形成铁（III）-铁载体复合物，然后通过诱导的 SbYS1（黄条纹 1）转运蛋白将其转运到根部。此外，在接种哈茨木霉后，缺铁时观察到几种植物过氧化物酶基因和脱落酸（ABA）的诱导，这可能有助于诱导对缺铁诱导的氧化应激和适应性反应的耐受。这是哈茨木霉在帮助缓解高粱缺铁症中的作用的第一个机制解释，并表明使用哈茨木霉的生物肥料将提高高 pH 环境中作物的铁供应。
