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Connective auxin transport contributes to strigolactone-mediated shoot branching control independent of the transcription factor BRC1.

ABSTRACT: The shoot systems of plants are built by the action of the primary shoot apical meristem, established during embryogenesis. In the axil of each leaf produced by the primary meristem, secondary axillary shoot apical meristems are established. The dynamic regulation of the activity of these axillary meristems gives shoot systems their extraordinary plasticity of form. The ability of plants to activate or repress these axillary meristems appropriately requires communication between meristems that is environmentally sensitive. The transport network of the plant hormone auxin has long been implicated as a central player in this tuneable communication system, with other systemically mobile hormones, such as strigolactone and cytokinin, acting in part by modulating auxin transport. Until recently, the polar auxin transport stream, which provides a high conductance auxin transport route down stems dominated by the auxin export protein PIN-FORMED1 (PIN1), has been the focus for understanding long range auxin transport in the shoot. However, recently additional auxin exporters with important roles in the shoot have been identified, including PIN3, PIN4 and PIN7. These proteins contribute to a wider less polar stem auxin transport regime, which we have termed connective auxin transport (CAT), because of its role in communication across the shoot system. Here we present a genetic analysis of the role of CAT in shoot branching. We demonstrate that in Arabidopsis, CAT plays an important role in strigolactone-mediated shoot branching control, with the triple pin3pin4pin7 mutant able to suppress partially the highly branched phenotype of strigolactone deficient mutants. In contrast, the branchy phenotype of mutants lacking the axillary meristem-expressed transcription factor, BRANCHED1 (BRC1) is unaffected by pin3pin4pin7. We further demonstrate that mutation in the ABCB19 auxin export protein, which like PIN3 PIN4 and PIN7 is widely expressed in stems, has very different effects, implicating ABCB19 in auxin loading at axillary bud apices.

SUBMITTER: van Rongen M

PROVIDER: S-EPMC6433298 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature

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Project description:Plant architecture greatly depends on its branching patterns. Branches are formed from meristems initiated in the axils of leaves. Axillary meristems may develop immediately giving new shoots or they may become arrested after a short period of growth as dormant axillary buds. This decision is affected by endogenous and environmental factors. We are studying two Arabidopsis genes coding for TCP transcription factors, BRANCHED1 (BRC1) and BRANCHED2 (BRC2) that control this key decision. Several endogenous and environmental stimuli affect this process one of them is the quality of ambient light. Plants have developed sophisticated mechanisms that allow them to detect the presence of nearby plants and trigger responses of development to avoid the shade. This set of responses is known as shade avoidance. One response to this syndrome, with high agronomic relevance, is the suppression of branching. The genetic basis of this response is still largely unknown. Our goal is to carry out, in Arabidopsis, a systematic study of the genetic control of the removal of branching during the escape response of the shadow. We found that Arabidopsis plants produce fewer branches when grown at high density. We also found that the removal of high-density branch is accompanied by up-regulation of BRC1. On the other hand, short light treatment enriched in far-red (which simulate the shade plant) also cause an accumulation of BRC1 mRNA levels in plants grown at low density. Besides initial data off transcriptomic analysis (wt vs. brc1-2) indicate that BRC1 could be involved in signaling / response to light in the axillary buds. In this study we have identified several potential target genes of BRC1 involved in the response to light. One is PIL2 (PHYTOCHROME INTERACTING FACTOR 3-LIKE 2), a gene that encodes a bHLH transcription factor that interacts with APRR1/TOC1. We are currently characterizing in more detail at the genetic and molecular level the BRC1 relationship with this and other potential target genes and their role in the control of branching patterns.

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Connective auxin transport contributes to strigolactone-mediated shoot branching control independent of the transcription factor BRC1.

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