Mutually opposing activity of PIN7 splicing isoforms is required for auxin‐mediated tropic responses in Arabidopsis thaliana

Abstract

Advanced transcriptome sequencing has revealed that the majority of eukaryotic genes undergo alternative splicing (AS). Nonetheless, little effort has been dedicated to investigating the functional relevance of particular splicing events, even those in the key developmental and hormonal regulators.Combining approaches of genetics, biochemistry and advanced confocal microscopy, we describe the impact of alternative splicing on the PIN7 gene in the model plant Arabidopsis thaliana. PIN7 encodes a polarly localized transporter for the phytohormone auxin and produces two evolutionarily conserved transcripts, PIN7a and PIN7b.PIN7a and PIN7b, differing in a four amino acid stretch, exhibit almost identical expression patterns and subcellular localization. We reveal that they are closely associated and mutually influence each other's mobility within the plasma membrane. Phenotypic complementation tests indicate that the functional contribution of PIN7b per se is minor, but it markedly reduces the prominent PIN7a activity, which is required for correct seedling apical hook formation and auxin-mediated tropic responses.Our results establish alternative splicing of the PIN family as a conserved, functionally relevant mechanism, revealing an additional regulatory level of auxin-mediated plant development.

How alternative splicing changes the properties of plant proteins

“…Moreover, PIN7a and PIN7b form homo- and heterodimers and show the rates of lateral mobility dropping closer to intermediate values when co-expressed ( Figure 2b ). Consistently, PIN7b reverts the exaggerated tropic response conferred by PIN7a , phenocopying that of the wild-type PIN7 allele (Kashkan et al, 2020 ; 2021 ).…”

“…For example, the BRC1a transcript ratios can change following various environmental stimuli (light conditions, decapitation, hormonal treatment) (Nicolas et al, 2015 ). Similarly, the levels of PIN7b or both BES1 isoforms can be changed by the application of the respective hormone, likely compensating the response to the growth regulator (Jiang et al, 2015 ; Kashkan et al, 2020 ; 2021 ).…”

TRIMETHYLGUANOSINE SYNTHASE1 mutations decanalize female germline development in Arabidopsis

“…The incomplete penetrance of the defects caused by the two tgs1 mutations reported here likely reflects functional redundancy involving paralogous TGS1‐LIKE genes or epistatic interactions involving unrelated, yet unknown genes. In regard to TGS1 regulatory function through splicing of genes required for sporogenesis in yeast (Qiu et al ., 2011), the critical role of alternative splicing in post‐transcriptional regulation of genes essential to plant reproduction (Cucinotta et al ., 2021; H. Li et al ., 2021; Kashkan et al ., 2022) might require TGS1, a hypothesis we are currently examining through RNAseq in reproductive tissues of A. thaliana .…”

Dynamic Dark Root Chamber: Advancing non-invasive phenotyping of roots kept in darkness using infrared imaging

“…IR LEDs seem to have no obvious effect on root fitness (Wells et al ., 2012; Shi et al ., 2018; Dermendjiev et al ., 2023). We were previously using IR LEDs to study growth dynamics of etiolated seedlings and we couldn’t distinguish growth behaviour from control plants in fully etiolated growth conditions (Kashkan, Garcia-González, et al ., 2022; Kashkan, Hrtyan, et al ., 2022). This approach can be used to monitor root outgrowth from germination, on agar plates, germination paper or soil, and to study various dynamic root traits and responses.…”