Shoot Branching Patterns Research Articles

Characterization of the Molecular Events Underlying the Establishment of Axillary Meristem Region in Pepper.

Plant architecture is a major motif of plant diversity, and shoot branching patterns primarily determine the aerial architecture of plants. In this study, we identified an inbred pepper line with fewer lateral branches, 20C1734, which was free of lateral branches at the middle and upper nodes of the main stem with smooth and flat leaf axils. Successive leaf axil sections confirmed that in normal pepper plants, for either node n, Pn (Primordium n) < 1 cm and Pn+1 < 1 cm were the critical periods between the identification of axillary meristems and the establishment of the region, whereas Pn+3 < 1 cm was fully developed and formed a completely new organ. In 20C1734, the normal axillary meristematic tissue region establishment and meristematic cell identity confirmation could not be performed on the axils without axillary buds. Comparative transcriptome analysis revealed that "auxin-activated signaling pathway", "response to auxin", "response to abscisic acid", "auxin biosynthetic process", and the biosynthesis of the terms/pathways, such as "secondary metabolites", were differentially enriched in different types of leaf axils at critical periods of axillary meristem development. The accuracy of RNA-seq was verified using RT-PCR for some genes in the pathway. Several differentially expressed genes (DEGs) related to endogenous phytohormones were targeted, including several genes of the PINs family. The endogenous hormone assay showed extremely high levels of IAA and ABA in leaf axils without axillary buds. ABA content in particular was unusually high. At the same time, there is no regular change in IAA level in this type of leaf axils (normal leaf axils will be accompanied by AM formation and IAA content will be low). Based on this, we speculated that the contents of endogenous hormones IAA and ABA in 20C1734 plant increased sharply, which led to the abnormal expression of genes in related pathways, which affected the formation of Ams in leaf axils in the middle and late vegetative growth period, and finally, nodes without axillary buds and side branches appeared.

Methods for Phenotyping Shoot Branching and Testing Strigolactone Bioactivity for Shoot Branching in Arabidopsis and Pea.

Shoot branching is a highly variable trait that evolves during plant development and is influenced by environmental and endogenous cues such as hormones. In particular, strigolactones (SLs) are hormones that play a key role in the control of shoot branching. Branch primordia, axillary buds formed in the leaf axils, display differential growth depending on their position in the plant and also respond to hormone signaling. In this chapter, we will describe how to quantify the degree of shoot branching in two plant model species, Arabidopsis and pea, commonly used to decipher the control of this complex trait. We will also propose several methods to perform treatments of SL or SL analogs, to investigate their bioactivity and effect on the shoot branching patterns of plants of different genotypes.

Axillary meristem initiation and bud growth in rice

The morphology of a plant is not predestined during embryonic development and its myriad branching architecture is post-embryonically determined by axillary meristem (AM) activity as the plant adapts to a varying environment. The shoot apical meristem produced during embryonic development repetitively gives rise to a phytomer that comprises a leaf, an AM, and an internode. The final aerial architecture is regulated by shoot branching patterns derived from AM activity. These branching patterns are modulated by two processes: AM formation and axillary bud outgrowth. Several transcription factors (TFs) that regulate these processes have been identified. Various plant hormones, including strigolactones and auxin, have major roles in controlling these TFs. In this review we focus on molecular mechanisms that guide AM initiation and axillary bud growth, using rice as our main species of emphasis.

Abstract 5122: Utilizing zebrafish to study the effect strigolactone on breast cancer cells

Abstract Strigolactones (SLs) are a novel class of phytohormones that regulates shoot branching patterns and above-ground plant architecture by inhibiting the outgrowth of axillary lateral buds or meristems. The SL analogues (SLAs) inhibit the growth and survival of a wide array of cancer-derived cell lines including: prostate, colon, lung, melanoma, osteosarcoma and leukemic cell lines, while minimally affecting normal cultured cells. Interestingly, cancer cells with high metastatic potential are more sensitive to the inhibitory effect of SLAs than less aggressive cells. Treatment of cancer cells with SLAs leads to the activation of stress-related signaling including p38MAPKs and JNK1/2, and disrupt the microtubule network. Furthermore, a reduction in acetylated-alpha-tubulin was observed in SLA-treated MDA-MB-231 cells. Microtubules dynamics has been proposed as one of the mechanisms that regulate cell migration by acting on lamellipodia formation. The ECIS invasion assay data suggests that even at low concentration of SLA and as soon as 6 hours, SLAs suppress MDA-MB-231 cells’ ability to invade the HUVEC monolayer. To further examine the effect of SLAs on the invasive and metastatic behaviors of cancer cells in vivo, fluorescently labeled MDA-MB-231 cells were used as xenograft models in zebrafish. Embryos injected with MDA-MB-231 cells showed 66.6% metastasis in vehicle treated control fishes, as compared to 22.85% in SLAs treated fishes. This suggests that SLAs are potent inhibitors of cancer dissemination and metastasis. Note: This abstract was not presented at the meeting. Citation Format: Kira Lin, Christopher Grivas, Elema Boru, Yaron Dayani, Eric Berens, Anna T. Riegel, Eric Glasgow, Ronit I. Yarden. Utilizing zebrafish to study the effect strigolactone on breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5122. doi:10.1158/1538-7445.AM2017-5122

Abscisic acid signaling is controlled by a BRANCHED1/HD-ZIP I cascade in Arabidopsis axillary buds

Shoot-branching patterns determine key aspects of plant life and are important targets for crop breeding. However, we are still largely ignorant of the genetic networks controlling locally the most important decision during branch development: whether the axillary bud, or branch primordium, grows out to give a lateral shoot or remains dormant. Here we show that, inside the buds, the TEOSINTE BRANCHED1, CYCLOIDEA, PCF (TCP) transcription factor BRANCHED1 (BRC1) binds to and positively regulates the transcription of three related Homeodomain leucine zipper protein (HD-ZIP)-encoding genes: HOMEOBOX PROTEIN 21 (HB21), HOMEOBOX PROTEIN 40 (HB40), and HOMEOBOX PROTEIN 53 (HB53). These three genes, together with BRC1, enhance 9-CIS-EPOXICAROTENOID DIOXIGENASE 3 (NCED3) expression, lead to abscisic acid accumulation, and trigger hormone response, thus causing suppression of bud development. This TCP/HD-ZIP genetic module seems to be conserved in dicot and monocotyledonous species to prevent branching under light-limiting conditions.

Quantitative trait loci analysis of lateral shoot growth in tomato

Branching is an important agronomic trait to determine plant architecture and fruit yield. In tomato, the regulatory mechanisms of shoot branching patterns have been studied mainly in mutants defective in meristem identity. Little is known about quantitative trait loci (QTLs) and their genetic interaction (epistasis) in lateral shoot development. Here, the genetic control of lateral bud outgrowth initiation and subsequent lateral bud development into branches were investigated. We used a BC1F7 population developed from Solanum lycopersicum (SL) and its close wild relative Solanum pimpinellifolium (SP) to measure the number of leaves on primary shoot (LN), the proportion of nodes with lateral buds (LS0) and lateral branches longer than 5cm (LS5) and 10cm (LS10) on main axis, the proportion of nodes with secondary lateral branches longer than 1cm (LSLS1) on primary lateral branches, and the lengths of the longest primary and secondary lateral branches (LLSL1 and LLSL2, respectively). Composite interval mapping detected 17 additive QTLs; those for LS5, LS10, and LLSL1 clustered near C2_At5g49480 or LEATPACb on chromosome 1 and LEOH361 on chromosome 4. One epistatic (QTL×QTL) interaction was identified for LS10 QTLs on chromosomes 1 and 12, where recombinant-type alleles increased lateral bud development into primary lateral branches. We analyzed further the QTLs clustered on chromosome 1 using two BC3F4 populations containing introgression region from the SP, which revealed the co-location of QTLs for lateral shoot development and days to flowering time. These results suggest that lateral shoot development is regulated by some additive and epistatic QTLs, some of which possibly exhibit a pleiotropic effect on flowering time.

Multiple pathways regulate shoot branching.

Shoot branching patterns result from the spatio-temporal regulation of axillary bud outgrowth. Numerous endogenous, developmental and environmental factors are integrated at the bud and plant levels to determine numbers of growing shoots. Multiple pathways that converge to common integrators are most probably involved. We propose several pathways involving not only the classical hormones auxin, cytokinins and strigolactones, but also other signals with a strong influence on shoot branching such as gibberellins, sugars or molecular actors of plant phase transition. We also deal with recent findings about the molecular mechanisms and the pathway involved in the response to shade as an example of an environmental signal controlling branching. We propose the TEOSINTE BRANCHED1, CYCLOIDEA, PCF transcription factor TB1/BRC1 and the polar auxin transport stream in the stem as possible integrators of these pathways. We finally discuss how modeling can help to represent this highly dynamic system by articulating knowledges and hypothesis and calculating the phenotype properties they imply.

Systematic Analysis of Branching Patterns of Three Almond Cultivars with Different Tree Architectures

Different almond (Prunus dulcis) cultivars have been characterized by their contrasting shoot branching patterns; however, the differences between patterns have been difficult to quantify. This study aimed to model the branching patterns of 2-year-old proleptic shoots on three almond cultivars (Nonpareil, Aldrich, and Winters) representing different tree architectures. The effects of branching pattern on flowering were also studied. The branching patterns of shoots of different length categories were assessed by a single hidden semi-Markov model for each cultivar. The models identified zones of homogeneous branching composition along shoots and were used to extract the occurrence and number of nodes of the zones according to shoot length categories. The numbers of flower buds were also determined for each shoot length category in each cultivar. The models of branching patterns of ‘Nonpareil’ and ‘Aldrich’ were similar and differed from the ‘Winters’ model. ‘Winters’ shoots produced more zones, but some of the zones had similar characteristics as previous zones and thus appeared to be repeated. This cultivar also had more spurs and sylleptic shoots than the other cultivars. The occurrence and node number of the central zones decreased along with reduction in shoot length in all the cultivars. ‘Aldrich’ tended to have more flower buds than comparable-length shoots of the other two cultivars. This study provides a quantitative description of the shoot branching patterns of three important cultivars and explains how branching changes in relation to shoot length, whereas production of flower buds varies despite similar branching patterns.

Regulation of shoot branching patterns by the basal root system: towards a predictive model

This study aimed to underpin the development of a generic predictive model of the regulation of shoot branching by roots in nodally rooting perennial prostrate-stemmed species using knowledge gained from physiological studies of Trifolium repens. Experiment 1 demonstrated that the net stimulatory influence from the basal rooted region of the plant on growth of newly emerging axillary buds on the primary stem decreased as their phytomeric distance from the basal root system increased. Experiment 2 found that at any one time the distribution of net root stimulus (NRS) to the apical bud on the primary stem and all lateral branches was fairly uniform within a single plant. Thus, although NRS availability was uniform throughout the shoot system at any point in time, it progressively decreased as shoot apical buds grew away from the basal root system. Based on these findings, a preliminary predictive model of the physiological regulation of branching pattern was developed. This model can explain the decline in growth rate of buds on a primary stem as it grows away from its basal root system but not the rapid progressive decline in secondary branch development on successive lateral branches. Thus knowledge of NRS availability to emerging buds is not, by itself, a sufficient basis from which to construct a predictive model. In addition, it seems that the ability of an emerging bud to become activated in response to its local NRS availability is, at least in part, directly influenced by the activation level of its parent apical bud. The experimental testing of this hypothesis, required for continued development of the model, is proceeding.

DWARF10, an RMS1/MAX4/DAD1 ortholog, controls lateral bud outgrowth in rice

Plant architecture is mostly determined by shoot branching patterns. Apical dominance is a well-known control mechanism in the development of branching patterns, but little is known regarding its role in monocots such as rice. Here, we show that the concept of apical dominance can be applied to tiller bud outgrowth of rice. In dwarf10 (d10), an enhanced branching mutant of rice, apical dominance can be observed, but the inhibitory effects of the apical meristem was reduced. D10 is a rice ortholog of MAX4/RMS1/DAD1 that encodes a carotenoid cleavage dioxygenase 8 and is supposed to be involved in the synthesis of an unidentified inhibitor of shoot branching. D10 expression predominantly occurs in vascular cells in most organs. Real-time polymerase chain reaction analysis revealed that accumulation of D10 mRNA is induced by exogenous auxin. Moreover, D10 expression is upregulated in six branching mutants, d3, d10, d14, d17, d27 and high tillering dwarf (htd1). No such effects were found for D3 or HTD1, the MAX2 and MAX3 orthologs, respectively, of rice. These findings imply that D10 transcription might be a critical step in the regulation of the branching inhibitor pathway. In addition, we present observations that suggest that FINE CULM1 (FC1), a rice ortholog of teosinte branched 1 (tb1), possibly works independently of the branching inhibitor pathway.

Influence of shoot architectural position on shoot growth and branching patterns in Cleyera japonica.

The influence of shoot architectural position on shoot growth and branching patterns was examined in saplings of Cleyera japonica Thunb. (Theaceae), an understory, broad-leaf evergreen woody species. Shoot length varied with branching order and the vertical position of the branch in the crown. In the upper crown, shoot length decreased with increasing branching order, whereas in the lower crown, differences in shoot length among branching orders were not significant. These results demonstrate that it is important to consider not only individual shoots, but also the relationships between shoots in terms of their architectural positions when studying the development of crown architecture in trees. Shoot branching patterns also varied with branching order and the vertical position of the branch in the crown. In the upper crown, branching was mainly sylleptic. In the middle of the crown, mainly proleptic branches were produced. In the lower crown, there was little branching. The importance of these trends in shoot growth and shoot branching patterns in terms of carbon production efficiency is discussed.