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Alfalfa pollen tube elongation in response to boron deficiency based on proteomics

ABSTRACT: Boron is an essential micronutrient for plant reproductive growth, and its key function in plants is mediated through cross-linking with the cell wall pectic polysaccharide rhamnogalacturonan II. As an important forage crop, boron deficiency in alfalfa inhibits pollen tube elongation, leading to floret abortion and reduced seed set. However, the molecular mechanism by which boron deficiency regulates pectin to affect alfalfa pollen-tube elongation remains unclear. In this study, we demonstrated that under boron-deficient conditions, methyl-esterified pectin shifts from an apical localization to subapical and shank regions, whereas deesterified pectin becames predominantly concentrated at the apex of pollen tubes. Proteomic analysis of pollen tubes subjected to different boron concentrations revealed significant enrichment of pectin methylesterase activity, polygalacturonase activity, and carbohydrate metabolic processes. Volcano plot analysis of the 56 shared differentially expressed proteins identified two pectin methylesterase inhibitors (MsPMEI14 and MsPMEI15). Chromosomal localization, phylogenetic, and cis-element analyses indicated that MsPMEI14 and MsPMEI15 were evolutionarily conserved. Subcellular localization showed that both MsPMEI14 and MsPMEI15 were localized in the cytoplasm, while MsPMEI14 was also localized in the nucleus, suggesting that MsPMEI14 might be the main factor responsible for the altered spatial distribution of pectin between the pollen tube apex and shank under low-boron conditions, phenotypic analysis demonstrated that mutation of PMEI suppresses pollen tube elongation under low-boron conditions.

ORGANISM(S): Medicago Sativa

SUBMITTER: Peisheng Mao

PROVIDER: PXD075180 | iProX | Wed Mar 04 00:00:00 GMT 2026

REPOSITORIES: iProX

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Project description:As in animals, cell-cell communication plays pivotal role in male-female recognition during plant sexual reproduction. Prelaid peptides secreted from the female reproductive tissues guide pollen tubes towards ovules for fertilization. However, the elaborate mechanisms for this dialogue have remained elusive, particularly from the male perspective. We perform genome-wide quantitative liquid chromatography coupled tandem mass spectrometry of a pistil-stimulated pollen tube secretome and identify 801 pollen tube-secreted proteins. Interestingly, in silico analysis reveals that the pollen tube-secretome is dominated by unconventional-type secreted proteins representing 57% of the total secretome. In support, we show that unconventional-type protein, translationally controlled tumor protein, is secreted to the apoplast. Remarkably, we discover that this protein could be secreted by infiltrating through the initial phases of the conventional secretory pathway and could reach the apoplast via exosomes as demonstrated by co-localization with Oleisin1 exosome marker. We demonstrate that Arabidopsis thaliana translationally controlled tumor protein-knockdown plants have pollen tubes that poorly navigate to the target ovule, and theÂ knocked down allele is poorly transmitted through the male. We show that regulators of the endoplasmic reticulum-trans-golgi network protein secretory pathway control secretion of pollen tube-secreted cysteine-rich proteins, including pollen tube attractants, and are essential for pollen tube growth and guidance, as well as ovule-targeting competence. This work, the first pollen tube secretome study, identifies novel genome-wide pollen tube-secreted proteins with potential function in pollen tube-ovule guidance for sexual reproduction. Functional analysis highlights a potential mechanism for pollen tube unconventional protein secretion and reveals likely regulators of pollen tube protein secretion. The association of pollen tube-secreted proteins with marker proteins shown to be secreted via exosomes in other species suggest secretion via exosomes as a possible mechanism for cell-cell communication between the pollen tube and female reproductive cells. For processed dataset with quantitative information, see Hafidh S, Potesil D, Fila J et al. Genome Bilogy 2016.

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Alfalfa pollen tube elongation in response to boron deficiency based on proteomics

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