| Summary: | Heterotrimeric G-proteins have been implicated in having a role in many plant signalling pathways. To understand further the role of G-proteins, a preliminary experiment was performed to assess the impact of the Gα subunit loss-of-function mutation <em>gpa1</em>-1 on the <em>Arabidopsis</em> transcriptome. The analysis indicated that the Gα subunit may play a role in response to jasmonic acid (JA). Consistent with this, Gα mutants showed a reduced response to JA in inhibition of chlorophyll accumulation and root growth, whilst Gα gain-of-function plants overexpressing Gα showed the opposite phenotype. The levels of JA and related compounds were unaffected in the <em>gpa1</em>-1 mutant, as was autoregulation of the <em>Allene Oxide Synthase</em> (<em>AOS</em>) gene that encodes a key enzyme for JA biosynthesis. In contrast, further analyses using Gα loss- and gain-of-function <em>Arabidopsis</em> lines indicated that Gα positively modulates the expression of the <em>Vegetative Storage Protein</em> (<em>VSP</em>) gene. This indicates that the Gα subunit regulates a subset of JA-regulated genes defining a branch point in this signalling pathway in <em>Arabidopsis</em>. Further analysis of the impact of Gα loss of function upon the JA-regulated transcriptome using <em>Arabidopsis</em> full genome arrays indicated that up to 29% of genes that are >2-fold regulated by JA in the wild type are misregulated in the Gα mutant. This supports the observation that a significant proportion of, but not all, JA-regulated gene expression is mediated by Gα.
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