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Tillering in rice (Oryza sativa) is one of the most important agronomic traits that determine grain yields. Previous studies on rice tillering mutants have shown that the outgrowth of tiller buds in rice is regulated by a carotenoid-derived MAX/RMS/D (more axillary branching) pathway, which may be conserved in higher plants. Strigolactones, a group of terpenoid lactones, have been recently identified as products of the MAX/RMS/D pathway that inhibits axillary bud outgrowth. We report here the molecular genetic characterization of d27, a classic rice mutant exhibiting increased tillers and reduced plant height. D27 encodes a novel iron-containing protein that localizes in chloroplasts and is expressed mainly in vascular cells of shoots and roots. The phenotype of d27 is correlated with enhanced polar auxin transport. The phenotypes of the d27 d10 double mutant are similar to those of d10, a mutant defective in the ortholog of MAX4/RMS1 in rice. In addition, 2'-epi-5-deoxystrigol, an identified strigolactone in root exudates of rice seedlings, was undetectable in d27, and the phenotypes of d27 could be rescued by supplementation with GR24, a synthetic strigolactone analog. Our results demonstrate that D27 is involved in the MAX/RMS/D pathway, in which D27 acts as a new member participating in the biosynthesis of strigolactones.

Strigolactones (SLs), a newly discovered class of carotenoid-derived phytohormones, are essential for developmental processes that shape plant architecture and interactions with parasitic weeds and symbiotic arbuscular mycorrhizal fungi. Despite the rapid progress in elucidating the SL biosynthetic pathway, the perception and signalling mechanisms of SL remain poorly understood. Here we show that DWARF 53 (D53) acts as a repressor of SL signalling and that SLs induce its degradation. We find that the rice ( Oryza sativa ) d53 mutant, which produces an exaggerated number of tillers compared to wild-type plants, is caused by a gain-of-function mutation and is insensitive to exogenous SL treatment. The D53 gene product shares predicted features with the class I Clp ATPase proteins and can form a complex with the α/β hydrolase protein DWARF 14 (D14) and the F-box protein DWARF 3 (D3), two previously identified signalling components potentially responsible for SL perception. We demonstrate that, in a D14- and D3-dependent manner, SLs induce D53 degradation by the proteasome and abrogate its activity in promoting axillary bud outgrowth. Our combined genetic and biochemical data reveal that D53 acts as a repressor of the SL signalling pathway, whose hormone-induced degradation represents a key molecular link between SL perception and responses. Strigolactones (SLs), key regulators of plant growth, are believed to mediate their responses through a proposed receptor (D14) that interacts with an F-box protein (D3) to form a D14–SCF D3 protein complex; here the perception of SLs by the D14–SCF D3 complex and the control of gene expression are linked by the finding that DWARF 53, a repressor protein of SL function, interacts with the D14–SCF D3 complex and is ubiquitinated and degraded in a SL-dependent manner. Strigolactone receptor identified The strigolactones are key regulators of plant growth, controlling the formation of secondary shoots and regulating root branching. Strigolactone responses are mediated through a proposed receptor (D14) that interacts with an F-box protein (D3). Now, in two related publications, Liang Jiang et al . and Feng Zhou et al . demonstrate a functional link between the perception of strigolactones by D14/D3 and the control of gene expression in rice. They show that the protein DWARF53 (D53), of previously unknown function, acts as a repressor of strigolactone signalling and that strigolactones induce its degradation. D53 interacts with the D14–D3 complex and is ubiquitinated and degraded by the proteasome in a strigolactone-dependent manner.

Overexpression of a microRNA in rice increases yield, suggesting new routes to crop improvement. Increasing grain yields is a major focus of crop breeders around the world. Here we report that overexpression of the rice microRNA (miRNA) OsmiR397, which is naturally highly expressed in young panicles and grains, enlarges grain size and promotes panicle branching, leading to an increase in overall grain yield of up to 25% in a field trial. To our knowledge, no previous report has shown a positive regulatory role of miRNA in the control of plant seed size and grain yield. We determined that OsmiR397 increases grain yield by downregulating its target, OsLAC , whose product is a laccase-like protein that we found to be involved in the sensitivity of plants to brassinosteroids. As miR397 is highly conserved across different species, our results suggest that manipulating miR397 may be useful for increasing grain yield not only in rice but also in other cereal crops.

Quantification of brassinosteroids is essential and extremely important to study the molecular mechanisms of their physiological roles in plant growth and development. Herein, we present a simple, material and cost-saving high-performance method for determining endogenous brassinosteroids (BRs) in model plants. This new method enables simultaneous enrichment of a wide range of bioactive BRs such as brassinolide, castasterone, teasterone, and typhasterol with ion exchange solid-phase extraction and high-sensitivity quantitation of these BRs based on isotope dilution combined with internal standard approach. For routine analysis, the consumption of plant materials was reduced to one-twentieth of previously reported and the overall process could be completed within 1 day compared with previous 3 to 4 days. The strategy was validated by profiling BRs in different ecotypes and mutants of rice (Oryza sativa) and Arabidopsis (Arabidopsis thaliana), and the BR distributions in different model plants tissues were determined with the new method. The method allows plant physiologists to monitor the dynamics and distributions of BRs with 1 gram fresh weight of model plant tissues, which will speed up the process for the molecular mechanism research of BRs with these model plants in future work.

• Although the role of auxin in biotrophic pathogenesis has been extensively studied, relatively little is known about its role in plant resistance to necrotrophs. • Arabidopsis thaliana mutants defective in different aspects of the auxin pathway are generally more susceptible than wild‐type plants to the necrotrophic pathogen Alternaria brassicicola. We show that A. brassicicola infection up‐regulates auxin biosynthesis and down‐regulates the auxin transport capacities of infected plants, these effects being partially dependent on JA signaling. We also show that these effects of A. brassicicola infection together lead to an enhanced auxin response in host plants. • Application of IAA and MeJA together synergistically induces the expression of defense marker genes PDF1.2 (PLANT DEFENSIN 1.2) and HEL (HEVEIN‐LIKE), suggesting that enhancement of JA‐dependent defense signaling may be part of the auxin‐mediated defense mechanism involved in resistance to necrotrophic pathogens. • Our results provide molecular evidence supporting the hypothesis that JA and auxin interact positively in regulating plant resistance to necrotrophic pathogens and that activation of auxin signaling by JA may contribute to plant resistance to necrotrophic pathogens.

Photoreceptor proteins utilise chromophores to sense light and trigger a biological response. The discovery that adenosylcobalamin (or coenzyme B 12 ) can act as a light-sensing chromophore heralded a new field of B 12 -photobiology. Although microbial genome analysis indicates that photoactive B 12 -binding domains form part of more complex protein architectures, regulating a range of molecular–cellular functions in response to light, experimental evidence is lacking. Here we identify and characterise a sub-family of multi-centre photoreceptors, termed photocobilins, that use B 12 and biliverdin (BV) to sense light across the visible spectrum. Crystal structures reveal close juxtaposition of the B 12 and BV chromophores, an arrangement that facilitates optical coupling. Light-triggered conversion of the B 12 affects quaternary structure, in turn leading to light-activation of associated enzyme domains. The apparent widespread nature of photocobilins implies involvement in light regulation of a wider array of biochemical processes, and thus expands the scope for B 12 photobiology. Their characterisation provides inspiration for the design of broad-spectrum optogenetic tools and next generation bio-photocatalysts. Photoreceptor proteins utilise biological chromophores to regulate a large range of cellular processes in response to light. Here the authors identify and characterise a sub-family of multi-centre photoreceptors, termed photocobilins, that not only utilise B 12 but also contain biliverdin (BV) as an additional chromophore.

Thellungiella salsuginea, a close relative of Arabidopsis , represents an extremophile model for abiotic stress tolerance studies. We present the draft sequence of the T. salsuginea genome, assembled based on ∼134-fold coverage to seven chromosomes with a coding capacity of at least 28,457 genes. This genome provides resources and evidence about the nature of defense mechanisms constituting the genetic basis underlying plant abiotic stress tolerance. Comparative genomics and experimental analyses identified genes related to cation transport, abscisic acid signaling, and wax production prominent in T. salsuginea as possible contributors to its success in stressful environments.

Natural plant-based flavonoids have drawn significant attention as dietary supplements due to their potential health benefits, including anti-cancer, anti-oxidant and anti-asthmatic activities. Naringenin, pinocembrin, eriodictyol and homoeriodictyol are classified as (2S)-flavanones, an important sub-group of naturally occurring flavonoids, with wide-reaching applications in human health and nutrition. These four compounds occupy a central position as branch point intermediates towards a broad spectrum of naturally occurring flavonoids. Here, we report the development of Escherichia coli production chassis for each of these key gatekeeper flavonoids. Selection of key enzymes, genetic construct design and the optimization of process conditions resulted in the highest reported titers for naringenin (484 mg/l), improved production of pinocembrin (198 mg/l) and eriodictyol (55 mg/l from caffeic acid), and provided the first example of in vivo production of homoeriodictyol directly from glycerol (17 mg/l). This work provides a springboard for future production of diverse downstream natural and non-natural flavonoid targets.

Background (Hydroxy)cinnamyl alcohols and allylphenols, including coniferyl alcohol and eugenol, are naturally occurring aromatic compounds widely utilised in pharmaceuticals, flavours, and fragrances. Traditionally, the heterologous biosynthesis of (hydroxy)cinnamyl alcohols from (hydroxy)cinnamic acids involved CoA-dependent activation of the substrate. However, a recently explored alternative pathway involving carboxylic acid reductase (CAR) has proven efficient in generating the (hydroxy)cinnamyl aldehyde intermediate without the need for CoA activation. In this study, we investigated the application of the CAR pathway for whole-cell bioconversion of a range of (hydroxy)cinnamic acids into their corresponding (hydroxy)cinnamyl alcohols. Furthermore, we sought to extend the pathway to enable the production of a variety of allylphenols and allylbenzene. Results By screening the activity of several heterologously expressed enzymes in crude cell lysates, we identified the combination of Segniliparus rugosus CAR (SrCAR) and Medicago sativa cinnamyl alcohol dehydrogenase (MsCAD2) as the most efficient enzymatic cascade for the two-step reduction of ferulic acid to coniferyl alcohol. To optimise the whole-cell bioconversion in Escherichia coli , we implemented a combinatorial approach to balance the gene expression levels of SrCAR and MsCAD2. This optimisation resulted in a coniferyl alcohol yield of almost 100%. Furthermore, we extended the pathway by incorporating coniferyl alcohol acyltransferase and eugenol synthase, which allowed for the production of eugenol with a titre of up to 1.61 mM (264 mg/L) from 3 mM ferulic acid. This improvement in titre surpasses previous achievements in the field employing a CoA-dependent coniferyl alcohol biosynthesis pathway. Our study not only demonstrated the successful utilisation of the CAR pathway for the biosynthesis of diverse (hydroxy)cinnamyl alcohols, such as p -coumaryl alcohol, caffeyl alcohol, cinnamyl alcohol, and sinapyl alcohol, from their corresponding (hydroxy)cinnamic acid precursors but also extended the pathway to produce allylphenols, including chavicol, hydroxychavicol, and methoxyeugenol. Notably, the microbial production of methoxyeugenol from sinapic acid represents a novel achievement. Conclusion The combination of SrCAR and MsCAD2 enzymes offers an efficient enzymatic cascade for the production of a wide array of (hydroxy)cinnamyl alcohols and, ultimately, allylphenols from their respective (hydroxy)cinnamic acids. This expands the range of value-added molecules that can be generated using microbial cell factories and creates new possibilities for applications in industries such as pharmaceuticals, flavours, and fragrances. These findings underscore the versatility of the CAR pathway, emphasising its potential in various biotechnological applications.

The allene oxide synthase (AOS) and hydroperoxide lyase (HPL) branches of the oxylipin pathway, which underlie the production of jasmonates and aldehydes, respectively, function in plant responses to a range of stresses. Regulatory crosstalk has been proposed to exist between these two signaling branches; however, there is no direct evidence of this. Here, we identified and characterized a jasmonic acid (JA) overproduction mutant, cea62, by screening a rice T-DNA insertion mutant library for lineages that constitutively express the AOS gene. Map-based cloning was used to identify the underlying gene as hydroperoxide lyase OsHPL3. HPL3 expression and the enzyme activity of its product, (E)-2-hexenal, were depleted in the cea62 mutant, which resulted in the dramatic overproduction of JA, the activation of JA signaling, and the emergence of the lesion mimic phenotype. A time-course analysis of lesion formation and of the induction of defense responsive genes in the cea62 mutant revealed that the activation of JA biosynthesis and signaling in cea62 was regulated in a developmental manner, as was OsHPL3 activity in the wild-type plant. Microarray analysis showed that the JA-governed defense response was greatly activated in cea62 and this plant exhibited enhanced resistance to the T1 strain of the bacterial blight pathogen Xanthomonasoryzaepvoryzae (Xoo). The wounding response was attenuated in cea62 plants during the early stages of development, but partially recovered when JA levels were elevated during the later stages. In contrast, the wounding response was not altered during the different developmental stages of wild-type plants. These findings suggest that these two branches of the oxylipin pathway exhibit crosstalk with regards to biosynthesis and signaling and cooperate with each other to function in diverse stress responses.