Recent advances in molecular phylogenetics and a series of important palaeobotanical discoveries have revolutionized our understanding of angiosperm diversification. Yet, the origin and early evolution of their most characteristic feature, the flower, remains poorly understood. In particular, the structure of the ancestral flower of all living angiosperms is still uncertain. Here we report model-based reconstructions for ancestral flowers at the deepest nodes in the phylogeny of angiosperms, using the largest data set of floral traits ever assembled. We reconstruct the ancestral angiosperm flower as bisexual and radially symmetric, with more than two whorls of three separate perianth organs each (undifferentiated tepals), more than two whorls of three separate stamens each, and more than five spirally arranged separate carpels. Although uncertainty remains for some of the characters, our reconstruction allows us to propose a new plausible scenario for the early diversification of flowers, leading to new testable hypotheses for future research on angiosperms.

The domestication of starch crops underpinned the development of human civilisation, yet we still do not fully understand how plants make starch. Starch is composed of glucose polymers that are branched (amylopectin) or linear (amylose). The amount of amylose strongly influences the physico-chemical behaviour of starchy foods during cooking and of starch mixtures in non-food manufacturing processes. The GRANULE-BOUND STARCH SYNTHASE (GBSS) is the glucosyltransferase specifically responsible for elongating amylose polymers and was the only protein known to be required for its biosynthesis. Here, we demonstrate that PROTEIN TARGETING TO STARCH (PTST) is also specifically required for amylose synthesis in Arabidopsis. PTST is a plastidial protein possessing an N-terminal coiled coil domain and a C-terminal carbohydrate binding module (CBM). We discovered that Arabidopsis ptst mutants synthesise amylose-free starch and are phenotypically similar to mutants lacking GBSS. Analysis of granule-bound proteins showed a dramatic reduction of GBSS protein in ptst mutant starch granules. Pull-down assays with recombinant proteins in vitro, as well as immunoprecipitation assays in planta, revealed that GBSS physically interacts with PTST via a coiled coil. Furthermore, we show that the CBM domain of PTST, which mediates its interaction with starch granules, is also required for correct GBSS localisation. Fluorescently tagged Arabidopsis GBSS, expressed either in tobacco or Arabidopsis leaves, required the presence of Arabidopsis PTST to localise to starch granules. Mutation of the CBM of PTST caused GBSS to remain in the plastid stroma. PTST fulfils a previously unknown function in targeting GBSS to starch. This sheds new light on the importance of targeting biosynthetic enzymes to sub-cellular sites where their action is required. Importantly, PTST represents a promising new gene target for the biotechnological modification of starch composition, as it is exclusively involved in amylose synthesis. Starch plays a vital role in our everyday lives. It is not only a major dietary carbohydrate, but is also used to manufacture household products such as pharmaceuticals, paper, and textiles. Plants produce starch as a means of storing energy; it is composed of two glucose polymers—amylopectin and amylose. While amylose is present in a smaller quantity than amylopectin, it has a major impact on starch processing. Being able to control the amount of amylose is therefore a goal for biotechnology. Amylose is made by the enzyme GRANULE BOUND STARCH SYNTHASE (GBSS), which was for decades believed to be the only protein required for amylose production. We now report here that a second protein, PROTEIN TARGETING TO STARCH (PTST), is involved in the process. Mutants lacking the PTST protein in the model plant Arabidopsis thaliana fail to make any amylose in starch. This is because the GBSS protein, which normally binds to starch, cannot bind in the absence of PTST. This discovery sheds new light on a previously unknown protein targeting process by which enzymes are delivered to the starch. Furthermore, our discovery highlights PTST an ideal target gene for biotechnology.

Summary: UV‐B radiation damage in leaves is prevented by epidermal UV‐screening compounds that can be modulated throughout ontogeny. In epiphytic orchids, roots need to be protected against UV‐B because they photosynthesize, sometimes even replacing the leaves. How orchid roots, which are covered by a dead tissue called velamen, avoid UV‐B radiation is currently unknown. We tested for a UV‐B protective function of the velamen using gene expression analyses, mass spectrometry, histochemistry, and chlorophyll fluorescence in Phalaenopsis × hybrida roots. We also investigated its evolution using comparative phylogenetic methods. Our data show that two paralogues of the chalcone synthase (CHS) gene family are UV‐B‐induced in orchid root tips, triggering the accumulation of two UV‐B‐absorbing flavonoids and resulting in effective protection of the photosynthetic root cortex. Phylogenetic and dating analyses imply that the two CHS lineages duplicated c. 100 million yr before the rise of epiphytic orchids. These findings indicate an additional role for the epiphytic orchid velamen previously thought to function solely in absorbing water and nutrients. This new function, which fundamentally differs from the mechanism of UV‐B avoidance in leaves, arose following an ancient duplication of CHS, and has probably contributed to the family's expansion into the canopy during the Cenozoic.

Two proteins present in leaf starch granules are important for the control of starch turnover, allowing plants to match the depletion of starch reserves to the

In contrast to most animals, plants have an indeterminate body plan, which allows them to add new body parts during their lifetime. A plant’s realized modular construction is the result of exogenous constraints and endogenous processes. This review focuses on endogenous processes that shape plant architectures and their evolution. The phylogenetic distribution of plant growth forms across the phylogeny implies that body architectures have originated and been lost repeatedly, being shaped by a limited set of genetic pathways. We (1) synthesize concepts of plant architecture, so far captured in 23 models; (2) extend them to the fossil record; (3) summarize what is known about their developmental genetics; (4) use a phylogenetic approach in several groups to infer how plant architecture has changed and by which intermediate steps; and (5) discuss which macroecological factors may constrain the geographic and ecological distribution of plant architectures. Dichotomously branching Paleozoic plants already encompassed a considerable diversity of growth forms, here captured in 12 new architectural models. Plotting the frequency of branching types through time based on an analysis of 58 927 land plant fossils revealed a decrease in dichotomous branching throughout the Devonian and Carboniferous, mirrored by an increase in other branching types including axillary branching. We suggest that the evolution of seed plant megaphyllous leaves enabling axillary branching contributed to the demise of dichotomous architectures. The developmental-genetic bases for key architectural traits underlying sympodial vs. monopodial branching, rhythmic vs. continuous growth, and axillary branching and its localization are becoming well understood, while the molecular basis of dichotomous branching and plagiotropy remains elusive. Three phylogenetic case studies of architecture evolution in conifers, Aloe and monocaulous arborescent vascular plants reveal relationships between architectural models and show that some are labile in given groups, whereas others are widely conserved, apparently shaped by ecological factors, such as intercepted sunlight, temperature, humidity and seasonality.