Plant hormones (Literature sources on phytohormones and plant signalling)

Authors: Efstathios Roumeliotis, Bjorn Kloosterman, Marian Oortwijn, Wouter Kohlen, Harro J. Bouwmeester, Christian W. B. Bachem and Richard G. F. Visser.

Potato Research (2022)

Abstract; "Auxin is known to be involved in various developmental processes, including meristem identity, shoot branching and initiation of potato tubers. The previously identified StYUCCA8 gene in potato that exhibits a peak in gene expression after tuber induction and prior to tuber swelling was cloned and over-expressed in order to study the effects of altered auxin content on shoot and stolon architecture and tuber development. The potato plants transformed with the 35S::StYUCCA8 construct exhibited increased shoot and stolon branching, reduced leaf size, lower average tuber fresh weight and enhanced adventitious and lateral root formation. Investigation of the IAA content revealed that the concentration of auxin was not altered in the shoot apex but was significantly lower in the basal part of the stem despite the several 100-fold increase of expression of the StYUCCA8 gene in three independent transgenic clones. This is the first time a potato YUCCA gene is used in an experiment in order to identify the role of endogenous auxin biosynthesis in potato plant development. Our research helps elucidate the importance of small changes of auxin content on several developmental events of the potato plant, such as shoot, stolon and root architecture."

Authors: Catriona H. Walker, Cara D. Wheeldon and Tom Bennett.

Plant Physiology (2021)

One-sentence summary: A series of negative feedback mechanisms regulate the spatio-temporal production of reproductive structures in Arabidopsis and Brassica napus, allowing plants to optimize seed-set.

Abstract: "The production of seed in flowering plants is complicated by the need to first invest in reproductive shoots, inflorescences, flowers, and fruit. Furthermore, in many species, it will be months between plants generating flowers and setting seed. How can plants therefore produce an optimal seed-set relative to environmental resources when the “reproductive architecture” that supports seed-set needs to be elaborated so far in advance? Here, we address this question by investigating the spatio-temporal control of reproductive architecture in Arabidopsis (Arabidopsis thaliana) and Brassica napus. We show that resource and resource-related signals such as substrate volume play a key role in determining the scale of reproductive effort, and that this is reflected in the earliest events in reproductive development, which broadly predict the subsequent reproductive effort. We show that a series of negative feedbacks both within and between developmental stages prevent plants from over-committing to early stages of development. These feedbacks create a highly plastic, homeostatic system in which additional organs can be produced in the case of reproductive failure elsewhere in the system. We propose that these feedbacks represent an “integrated dominance” mechanism that allows resource use to be correctly sequenced between developmental stages to optimize seed set."

Authors: Xiaoying Wei, Jun Yang, Dou Lei, Hao Feng, Zhenan Yang, Guoqin Wen, Zhuoyuan He, Wenjing Zeng and Jian Zou.

Plant Cell Reports (2021)

Key message: The SlTCP26 negatively regulated auxin signal to relieve the apical dominance and suppressed abscisic acid signal to remove the lateral bud dormancy, promoting lateral branches development. 

Abstract: "Lateral branches formation from lateral buds is a complex regulatory process in higher plants, and the interaction between transcription factors and hormones is indispensable during this process. TCP transcription factors have been reported to regulate lateral branches development, while the detailed function, especially interacting with auxin and ABA during this process, was still ambiguous in tomato. In this study, a branch regulatory gene, SlTCP26, was identified in tomato, and its role along with its interaction to hormones during branch development, as investigated. The results indicated that overexpression of SlTCP26 would promote lateral branches development, and could suppress the expressing of the genes associated with IAA signaling, presenting similar effects in decapitated plants. Conversely, the exogenous IAA application could inhibit the expression of SlTCP26. Furthermore, the expressing of the ABA signaling-related genes was inhibited in SlTCP26 overexpressed tomato, similar to that in decapitated tomato. Our findings suggested that SlTCP26 may be a crucial adjuster for synergistic action between ABA and IAA signals during the development of lateral branches, and it could promote the lateral buds grow into lateral shoots, via inhibiting IAA signal to relieve the apical dominance and suppressing ABA signal to remove the lateral bud dormancy. Our study provided some insights for the development of tomato lateral branches to understand the apical dominance regulatory network."

Authors: Ying He, Liuyu Li and Dagang Jiang.

Plant Molecular Biology Reporter (2021)

Abstract: "Rice is one of the most important crops worldwide, whose yield is vital to human nutrition in the context of a rapidly growing world population. Plant architecture significantly affects grain yield, which is to a large extent determined by tiller angle and tiller number. Tiller angle is the angle between the primary tiller and the main culm. Its regulation is complex and is influenced by multiple environmental and genetic factors. This review provides an overview of the regulation of tiller angle in rice, with particular focus on the roles of the growth environment and method of cultivation; phytohormones such as auxin, gibberellins, and strigolactones; gravity; and genes related to the control of tiller angle. The major research foci and the outlook for research into the regulation of tiller angle in rice are discussed."

Authors: Victoria M. R. Spencer, Lucy Bentall and C. Jill Harrison.

Development (2023)

Abstract: "Diverse branching forms have evolved multiple times across the tree of life to facilitate resource acquisition and exchange with the environment. In the vascular plant group, the ancestral pattern of branching involves dichotomy of a parent shoot apex to form two new daughter apices. The molecular basis of axillary branching in Arabidopsis is well understood, but few regulators of dichotomous branching are known. Through analyses of dichotomous branching in the lycophyte, Selaginella kraussiana, we identify PIN-mediated auxin transport as an ancestral branch regulator of vascular plants. We show that short-range auxin transport out of the apices promotes dichotomy and that branch dominance is globally coordinated by long-range auxin transport. Uniquely in Selaginella, angle meristems initiate at each dichotomy, and these can develop into rhizophores or branching angle shoots. We show that long-range auxin transport and a transitory drop in PIN expression are involved in angle shoot development. We conclude that PIN-mediated auxin transport is an ancestral mechanism for vascular plant branching that was independently recruited into Selaginella angle shoot development and seed plant axillary branching during evolution."

Authors: Da Cao, François Barbier, Elizabeth A. Dun, Franziska Fichtner, Lili Dong, Stephanie C. Kerr and Christine A Beveridge.

bioRxiv (2022)

Abstract: "The inhibition of shoot branching by the growing shoot tip of plants, termed apical dominance, was originally thought to be mediated by auxin. Recently the importance of the shoot tip sink strength during apical dominance has re-emerged with recent studies highlighting roles for sugars in promoting branching. This raises many unanswered questions on the relative roles of auxin and sugars in apical dominance. Here we show that auxin regulation of cytokinins, which promote branching, is significant only after an initial stage of branching we call bud release. During this early bud release stage, rapid cytokinin increases are associated with enhanced sugars. Auxin may also act through strigolactones which have been shown to suppress branching after decapitation, but here we show that strigolactones do not have a significant effect on initial bud outgrowth after decapitation. We report here that when sucrose or cytokinin is abundant, strigolactones are less inhibitory during the bud release stage compared to later stages and that strigolactone treatment rapidly inhibits cytokinin accumulation in pea axillary buds of intact plants. After initial bud release, we find an important role of gibberellin in promoting sustained bud growth downstream of auxin. We are therefore able to suggest a model of apical dominance that integrates auxin, sucrose, strigolactones, cytokinins and gibberellins and describes differences in signalling across stages of bud release to sustained growth."

Authors: Elizabeth García-Cárdenas, Randy Ortiz-Castro, León Francisco Ruiz-Herrera, Eduardo Valencia-Cantero and José López-Bucio.

Protoplasma (2021)

Abstract: "The interaction of plant roots with bacteria is influenced by chemical signaling, where auxins play a critical role. Auxins exert positive or negative influences on the plant traits responsible of root architecture configuration such as root elongation and branching and root hair formation, but how bacteria that modify the plant auxin response promote or repress growth, as well as root structure, remains unknown. Here, we isolated and identified via molecular and electronic microscopy analysis a Micrococcus luteus LS570 strain as a plant growth promoter that halts primary root elongation in Arabidopsis seedlings and strongly triggers root branching and absorptive potential. The root biomass was exacerbated following root contact with bacterial streaks, and this correlated with inducible expression of auxin-related gene markers DR5:GUS and DR5:GFP. Cellular and structural analyses of root growth zones indicated that the bacterium inhibits both cell division and elongation within primary root tips, disrupting apical dominance, and as a consequence differentiation programs at the pericycle and epidermis, respectively, triggers the formation of longer and denser lateral roots and root hairs. Using Arabidopsis mutants defective on auxin signaling elements, our study uncovers a critical role of the auxin response factors ARF7 and ARF19, and canonical auxin receptors in mediating both the primary root and lateral root response to M. luteus LS570. Our report provides very basic information into how actinobacteria interact with plants and direct evidence that the bacterial genus Micrococcus influences the cellular and physiological plant programs ultimately responsible of biomass partitioning."

Author: Madeleine Seale.

Plant Physiology (2021)

Excerpts: "In this issue of Plant Physiology, Walker, Wheeldon, and Bennett have untangled the relationships between different aspects of reproductive architecture and concluded that both Arabidopsis thaliana and Brassica napus tend to maintain a consistent number of shoot inflorescences and fruits regardless of developmental trajectory."

"In both species examined, the inherent developmental characteristics, such as plant size and shoot architecture, determine reproductive allocation. These traits are also affected though by environmental factors, such as nutrients and resources (Wheeldon et al., 2021)."

"Plasticity in shoot architecture is closely connected to apical dominance relationships between shoot meristems (Bangerth, 1989). To understand this further, Walker et al. (2021) carried out a set of architectural perturbations (Figure 1A)."

"The data presented provide a framework for understanding reproductive shoot architecture (Figure 1B) in Brassicaceae and open up a number of developmental and mechanistic questions.......What are the signaling mechanisms underlying reproductive coordination? The latter seems likely to be integrated within the auxin–strigolactone–cytokinin signaling mechanisms already well-described for apical dominance (Barbier et al., 2019; Domagalska and Leyser, 2011; Waldie et al., 2014), but this has not been extensively investigated in terms of reproductive architecture."

Authors: Jinyang Lyu, Yuan Guo, Chunlei Du, Haibo Yu, Lijian Guo, Li Liu, Xinfa Wang, Huixian Zhao and Shengwu Hu.

Research Square (2021)

Abstract: "Plant architecture is very important for rapeseed breeding. Here, we reported an ETHYLENE RESPONSE FACTOR (ERF) transcription factor BnERF114.A1 of Brassica napus participating in plant architecture regulation. BnERF114.A1 is a member of ERF family group x-a, encoding a putative protein of 252 aa which consisting of an AP2/ERF domain and a conserved CMX-1 motif. BnERF114.A1 located in nucleus and had transcriptional activity with its functional region located in 142 aa ~ 252 aa of its C-terminus. The GUS staining analysis revealed that BnERF114.A1 highly expressed in leaf primordia, shoot apical meristem, leaf marginal meristem, and reproductive organs. Ectopic expression of BnERF114.A1 in Arabidopsis reduced plant height, increased branch numbers and silique numbers per plants, and finally increased seed yield per plant. Further investigation demonstrated that overexpression of BnERF114.A1 can inhibit IAA efflux and cause accumulation of auxin in apex, and arrest apical dominance in Arabidopsis. The findings suggested BnERF114.A1 could provide a candidate gene for rapeseed plant architecture molecular breeding."