Apple Gene MhLHCA2 Helps Plants Survive Iron-Starved Soils, Study Finds

Iron is one of those nutrients that plants cannot live without, yet in many of the world’s agricultural soils it is maddeningly hard to obtain. In calcareous and alkaline conditions, which cover vast stretches of orchard land in China and beyond, iron locks into insoluble mineral forms that roots simply cannot absorb. The result is iron deficiency chlorosis: leaves yellow, photosynthesis falters, fruit quality declines and yields drop. For apple growers, whose trees often sit on alkaline rootstocks in marginal soils, the problem is chronic and expensive. Now a team of researchers at Gansu Agricultural University, working with colleagues at the Chinese Academy of Forestry and Northwest A&F University, has identified a gene that appears to help apple tissue cope with iron starvation on several fronts at once. The gene, called MhLHCA2, is described in a study published in BMC Plant Biology, and its effects touch everything from antioxidant defenses to the efficiency of photosystem I, one of the two light-harvesting engines of photosynthesis.

The name LHCA2 offers a clue to what the protein normally does. LHCA genes encode light-harvesting complex proteins associated with photosystem I, the pigment-protein machinery that accepts electrons from plastocyanin and uses light energy to drive them onward to ferredoxin. Iron is deeply woven into that machinery: photosystem I itself carries iron-sulfur clusters, ferredoxin is an iron-containing protein, and the entire electron transport chain depends on cytochromes built around iron atoms. When iron runs short, the photosynthetic apparatus is among the first casualties, which is why iron-starved plants so often show pale leaves and depressed photosynthetic efficiency. What makes the new study interesting is the suggestion that a structural component of photosystem I, MhLHCA2, does more than simply hold chlorophyll in place. According to the authors’ evidence, it also participates in the broader physiological response that plants mount when iron becomes scarce.

To probe that role, the researchers took a two-pronged approach that combined gain-of-function and loss-of-function evidence. On one side, they generated stable apple callus lines, masses of undifferentiated cells grown in culture, that overexpress MhLHCA2. Calli are a workhorse of plant molecular biology because they can be maintained under precisely controlled nutrient conditions and compared genetically identical except for the transgene of interest. On the other side, the team used virus-induced gene silencing, or VIGS, to knock down MhLHCA2 expression transiently in whole apple seedlings. VIGS hijacks a plant viral vector to trigger the plant’s own RNA silencing machinery, dampening the target gene without producing a permanent transgenic line. Together, the two systems allowed the researchers to ask what happens when the gene is present in excess and when it is partially removed, under both iron-sufficient and iron-deficient conditions.

The overexpression experiments produced a strikingly consistent picture. When iron was withheld, all callus lines suffered a decline in the activities of three key antioxidant enzymes: superoxide dismutase, or SOD, peroxidase, or POD, and catalase, or CAT. These enzymes form the front line of defense against reactive oxygen species, the chemically aggressive molecules that accumulate when photosynthetic electron transport is disrupted and that damage membranes, proteins and DNA. But the MhLHCA2-overexpressing calli weathered the deficit noticeably better than wild-type controls. They retained higher SOD and CAT activities, accumulated lower levels of reactive oxygen species, and showed reduced concentrations of malondialdehyde, or MDA, a standard chemical marker of lipid peroxidation and membrane damage. In other words, extra MhLHCA2 seemed to buffer the oxidative stress that iron starvation normally inflicts on plant cells.

The benefits did not stop at antioxidant protection. The overexpressing calli also displayed a suite of changes pointing toward enhanced iron acquisition and mobilization. They showed higher ferric-chelate reductase activity, an enzymatic reaction that reduces poorly soluble ferric iron, Fe3+, to the far more absorbable ferrous form, Fe2+, at the root surface. This reaction is the defining feature of the strategy I iron-acquisition mechanism used by apple and other non-graminaceous plants. Consistent with that, the overexpressing lines accumulated more Fe2+ and more total iron, along with higher levels of water-extractable iron, the fraction most readily available for metabolic use. The researchers also observed elevated expression of several genes known to respond to iron deficiency, suggesting that MhLHCA2 overexpression primes the plant’s iron-starvation transcriptional program rather than bypassing it.

The silencing experiments in seedlings told the complementary story from the opposite direction. When MhLHCA2 expression was knocked down under iron-deficient conditions, the seedlings’ photosynthetic performance deteriorated measurably. The researchers documented increased donor-side limitation of photosystem I, meaning the reaction center could not be supplied with electrons quickly enough from its upstream donors, and reduced photochemical efficiency overall. These impairments are physiologically coherent: with less of the LHCA2 light-harvesting protein available, photosystem I’s capacity to capture and channel light energy would be expected to suffer, and iron scarcity compounds the problem by starving the complex of the iron-sulfur clusters and ferredoxin it needs. The silenced seedlings also accumulated more reactive oxygen species, showed lower ferric-chelate reductase activity, carried reduced iron contents in their tissues and developed restricted root systems, all of which are hallmarks of a plant struggling to cope with iron shortage.

Taken together, the two experimental arms support a model in which MhLHCA2 sits at the intersection of photosynthesis and iron physiology. A well-maintained photosystem I presumably sustains the energy supply and redox balance that iron-deficient plants need to fuel their acquisition machinery, including the proton extrusion and ferric reduction that acidify the rhizosphere and solubilize iron. At the same time, the gene’s influence on antioxidant enzyme activities suggests it may help stabilize the redox environment of the chloroplast, limiting the oxidative cascade that iron deficiency typically triggers. The elevated expression of iron-deficiency-responsive genes in overexpressing lines hints at a signaling dimension as well, though the precise molecular mechanism linking an antenna protein to iron homeostasis remains to be worked out.

The authors are careful about the limits of their evidence, and that caution matters. Callus cultures, however convenient, are undifferentiated tissues grown in artificial media, and transient VIGS silencing produces only partial, temporary knockdown in seedlings. Neither system can fully replicate the physiology of a mature tree responding to iron-poor soil over a growing season. The study explicitly notes that these experimental systems do not replace stable whole-plant genetic validation, and that regenerated stable overexpression and loss-of-function plants will be required to establish the long-term contribution of MhLHCA2 to whole-plant iron-deficiency tolerance and iron acquisition. In a field where promising callus phenotypes sometimes fail to translate into field-ready traits, that restraint is appropriate.

Even so, the practical implications are considerable. Iron deficiency chlorosis is routinely managed with soil amendments and foliar iron sprays, interventions that are costly, must be repeated and often deliver only partial relief because applied iron rapidly reverts to insoluble forms in alkaline soils. A genetic lever that improves a plant’s own iron acquisition and protects its photosynthetic machinery under scarcity would be a more durable solution. If MhLHCA2 or its regulatory network can be harnessed in breeding programs, either through marker-assisted selection for favorable alleles or through targeted genome editing, apple rootstocks and scions with better tolerance of calcareous soils could follow. The gene’s connection to photosynthetic efficiency adds a further incentive, since any improvement in iron use under stress would likely translate directly into better growth and fruit production.

The study also adds to a growing appreciation that light-harvesting proteins are not passive structural components but active participants in stress physiology. As researchers continue to dissect how antenna proteins communicate with nutrient-signaling pathways, genes like MhLHCA2 may reveal new points of control for crop improvement. For now, the Gansu team’s findings, funded by the National Natural Science Foundation of China and provincial research programs in Gansu, provide the clearest evidence yet that this photosystem I component contributes to apple’s response to iron deficiency, and they lay the groundwork for the whole-plant validation experiments that will determine whether the discovery can move from the culture dish to the orchard.

Subject of Research: The role of the MhLHCA2 gene in apple responses to iron deficiency stress

Article Title: MhLHCA2 contributes to apple responses to iron deficiency by supporting photosynthetic performance and Fe-related physiological processes

Article References: Li, W., Zhang, Z., Dong, Y., Wang, X., Gao, Y., Xian, X., & Wang, Y. (2026). MhLHCA2 contributes to apple responses to iron deficiency by supporting photosynthetic performance and Fe-related physiological processes. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09970-0

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09970-0

Keywords: MhLHCA2, apple, iron deficiency, photosystem I, photosynthesis, reactive oxygen species, antioxidant enzymes, ferric-chelate reductase, virus-induced gene silencing, plant physiology, calcareous soils, BMC Plant Biology