Low Red Light:Far Red Light Inhibits Branching by Promoting Auxin Signaling
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Low Red Light:Far Red Light Inhibits Branching by Promoting Auxin Signaling Srinidhi V. Holalu1,2 · Srirama K. Reddy2,3 · Scott A. Finlayson2 Received: 21 May 2020 / Accepted: 14 October 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The branching trait is influenced by various environmental signals, including the Red light:Far Red light (R:FR), an indicator of competition and an inhibitor of axillary bud growth. Branch development is influenced by an array of hormones, including auxin which indirectly suppresses bud growth as a consequence of auxin transport and signaling in the main stem. The suppressive effect of auxin sourced from the shoot apex and transported basipetally is a major mechanism contributing to apical dominance, a form of correlative inhibition where superior growing points restrict the growth of those lower on the plant. The current study shows that increased apical dominance is a mechanism that suppresses the branching of plants grown in a low R:FR. The elevated apical dominance was not due to increased levels of the natural auxin IAA, but was associated with enhanced expression of auxin-induced genes both in the presence and absence of exogenous auxin. A direct test of bud sensitivity to auxin confirmed that a low R:FR promoted auxin responsiveness leading to reduced bud growth. Thus, the low R:FR enhancement of auxin sensitivity is a mechanism that contributes to the reduced branching phenotype of plants growing in competitive environments. Keywords Branching · Red light:far red light · Auxin · Phytochrome
Introduction Plants display enormous diversity in above-ground architectural traits and variation in axillary branching patterns effectively generates a spectrum of plant forms. Axillary meristems formed in leaf axils develop into buds, and the buds may grow out to form a branch/tiller or remain dormant/semi-dormant. Branching is an important trait that was often selected for during domestication of major crops and has been modified by modern breeding programs in both annuals and perennials (Dong et al. 2019). The manipulation of branching by pruning off terminal shoots is a recurring * Scott A. Finlayson [email protected] 1
Department of Plant and Microbial Biology, UC, Berkeley, CA 94720, USA
2
Department of Soil and Crop Sciences, Faculty of Molecular and Environmental Plant Sciences, Texas A&M University and Texas A&M AgriLife Research, College Station, TX 77843, USA
3
Biorational Research Center, Valent BioSciences LLC, 1910 Innovation Way, Suite 1, Libertyville, IL 60048, USA
operation to improve productivity in orchards (Lauri et al. 2009). Shoot branching is thought to optimize resource allocation in response to biotic and abiotic stresses in natural populations occupying diverse ecological landscapes (Baker et al. 2012; Remington et al. 2015). The plasticity in bud outgrowth offers a wide range of possible plant forms from prolific branching to a complete absence of branches and all possibilities in between. Genetic facto
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