Proteomic identification of gravitropic response genes in peanut gynophores.

Peanut (Arachis hypogaea L.) is one of the most important oil-bearing crops in the world. The gravitropic response of peanut gynophores plays an essential role in peanut reproductive development. In this study, we developed an in vitro culture system and applied it to the study of peanut gynophore gravitropism. By comparing the proteomes of gynophores grown in vitro with the tip pointing upward (gravity stimulation sample) and downward (natural growth control) at 6h and 12h, we observed 42 and 39 with significantly altered expression pattern at 6 and 12h, respectively. Out of these proteins, 13 proteins showed same expression profiling at both 6h and 12h. They were identified by MALDI-TOF/TOF and further characterized with quantitative real time RT-PCR. Among the 13 identified proteins, two were identified as class III acidic endochitinases, two were identified as Kunitz trypsin protease inhibitors, and the remaining proteins were identified as pathogenesis-related class 10 protein, Ara h 8 allergen isoform 3, voltage-dependent anion channel, gamma carbonic anhydrase 1, germin-like protein subfamily 3 member 3 precursor, chloride channel, glycine-rich RNA-binding protein and gibberellin receptor GID1. Real time RT-PCR analysis revealed that transcriptional regulation is consistent with expression at the protein level for class III acidic endochitinase, Kunitz trypsin protease inhibitor, chloride channel and pathogenesis-related class 10 protein, while the expression of the other 7 proteins might be regulated at post-transcriptional levels. This study identified several potential gravitropic response proteins in peanut gynophores and helps to understand early gravitropic responses in peanut gynophores. BIOLOGICAL SIGNIFICANCE: The gravitropic response of the peanut gynophores plays an essential role in peanut production. However, the molecular mechanism responsible for gravitropic responses in the peanut gynophores has not been explored yet. The result generated in this study may provide in vitro culture system for gravitropism study of plant gravitropic response and novel insights into the proteome-level response and give a more comprehensive understanding of early gravitropic response in peanut gynophores. This article is part of a Special Issue entitled: Translational Plant Proteomics.

Transcriptome profiling of peanut (Arachis hypogaea) gynophores in gravitropic response.

Peanut (Arachis hypogaea L.) produces flowers aerially, but the fruit develops underground. This process is mediated by the gynophore, which always grows vertically downwards. The genetic basis underlying gravitropic bending of gynophores is not well understood. To identify genes related to gynophore gravitropism, gene expression profiles of gynophores cultured in vitro with tip pointing upward (gravitropic stimulation sample) and downward (control) at both 6 and 12h were compared through a high-density peanut microarray. After gravitropic stimulation, there were 174 differentially expressed genes, including 91 upregulated and 83 downregulated genes at 6h, and 491 differentially expressed genes including 129 upregulated and 362 downregulated genes at 12h. The differentially expressed genes identified were assigned to 24 functional categories. Twenty pathways including carbon fixation, aminoacyl-tRNA biosynthesis, pentose phosphate pathway, starch and sucrose metabolism were identified. The quantitative real-time PCR analysis was performed for validation of microarray results. Our study paves the way to better understand the molecular mechanisms underlying the peanut gynophore gravitropism.