How Strigolactones Help Apple Trees Resist Aluminum Stress

Jim Crocker
4th April, 2024

How Strigolactones Help Apple Trees Resist Aluminum Stress

Image Source: Natural Science News, 2024

Key Findings

  • In apple orchards, a study found a way to protect trees from soil aluminum toxicity
  • A synthetic hormone helped apple trees store aluminum safely, preventing root damage
  • Researchers identified genes that when altered, increase aluminum tolerance in apples
Apple orchards worldwide face a significant challenge due to soil acidification, which can lead to aluminum toxicity. This is a pressing issue, as aluminum can poison the roots of apple trees, leading to poor growth and reduced fruit yield. Researchers at Qingdao Agricultural University have recently made a breakthrough in understanding how to protect apple trees from this environmental stress[1]. Strigolactones (SLs), plant hormones known for their role in plant architecture and symbiotic relationships with fungi[2], have now been implicated in the plant's response to aluminum stress. The study by Qingdao Agricultural University found that treating apple rootstock with GR24, a synthetic SL, significantly reduced the damage caused by aluminum chloride (AlCl3), a compound that simulates aluminum toxicity in the soil. GR24 was effective in two main ways: it prevented aluminum from moving across the cell wall and facilitated the storage of aluminum in the vacuoles, which are compartments within the cell that can contain and neutralize toxins. The study went further to unravel the genetic mechanisms behind this protective effect. Through RNA sequencing (RNA-seq), a method used to observe the presence and quantity of RNA in a biological sample, the researchers pinpointed a key transcription factor gene, MdWRKY53, that when overexpressed, increased the aluminum tolerance in transgenic apple plants. Transcription factors are proteins that help turn specific genes on or off by binding to nearby DNA. Following the genetic trail, the team used a technique known as chromatin immunoprecipitation followed by sequencing (ChIP-seq) to identify two genes regulated by MdWRKY53: MdPMEI45, which encodes a protein that inhibits enzymes affecting the cell wall, and MdALS3, which encodes an aluminum transporter. These two genes are central to the apple tree's defense against aluminum. GR24 was shown to promote the interaction between MdWRKY53 and another transcription factor, MdTCP15, which in turn increased the activity of MdPMEI45. This activity is crucial for preventing aluminum from entering the cells. Meanwhile, MdWRKY53 also boosted the expression of MdALS3, which helps sequester aluminum safely within the vacuoles. These findings suggest that there are two distinct but complementary modules at work in apple trees to combat aluminum stress: the SL-WRKY+TCP-PMEI module, which blocks the entry of aluminum into cells, and the SL-WRKY-ALS module, which aids in the internal detoxification of aluminum. This dual mechanism provides a two-pronged strategy for enhancing aluminum tolerance in apple trees. Previous research has demonstrated the complexity of plant hormone signaling and the extensive crosstalk that occurs between different pathways[3]. This current study builds on that knowledge by showing how SLs can influence other hormonal pathways to confer stress resilience. It also confirms the role of SLs in directly regulating bud growth, as seen in studies of the PsBRC1 gene in peas[4], by illustrating a similar regulatory capacity in apple trees under stress. These insights into the molecular interactions between SLs and other plant hormones open up new avenues for developing apple varieties with enhanced tolerance to aluminum toxicity. By manipulating the SL pathway and the MdWRKY53 transcription factor, it may be possible to breed or genetically engineer apple trees that are better equipped to withstand the challenges of acidic soils. The practical applications of this research could lead to more sustainable apple production and help maintain the health of orchards in the face of environmental stressors.

BiochemPlant ScienceAgriculture

References

Main Study

1) Strigolactones alleviate AlCl3 stress by vacuolar compartmentalization and cell wall blocking in apple.

Published 2nd April, 2024

https://doi.org/10.1111/tpj.16753

Related Studies

2) Strigolactones, a novel carotenoid-derived plant hormone.

https://doi.org/10.1146/annurev-arplant-043014-114759

3) Extensive signal integration by the phytohormone protein network.

https://doi.org/10.1038/s41586-020-2460-0

4) The pea TCP transcription factor PsBRC1 acts downstream of Strigolactones to control shoot branching.

https://doi.org/10.1104/pp.111.182725


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