Different plasticity of bud outgrowth at cauline and rosette nodes in Arabidopsis thaliana

Shoot branching is a complex mechanism in which secondary shoots grow from buds that are initiated from meristems established in leaf axils. The model plant Arabidopsis thaliana has a rosette leaf growth pattern in the vegetative stage. After flowering initiation, the main stem starts to elongate with the top leaf primordia developing into cauline leaves. Meristems in arabidopsis are initiated in the axils of rosette or cauline leaves, giving rise to rosette or cauline buds, respectively. Plasticity in the process of shoot branching is regulated by resource and nutrient availability as well as by plant hormones. However, few studies have attempted to test whether cauline and rosette branching are subject to the same plasticity. Here, we addressed this question by phenotyping cauline and rosette branching in three arabidopsis ecotypes and several arabidopsis mutants with varied shoot architectures. Our results show that there is no negative correlation between cauline and rosette branch numbers in arabidopsis, demonstrating that there is no trade-off between cauline and rosette bud outgrowth. Through investigation of the altered branching pattern of flowering pathway mutants and arabidopsis ecotypes grown in various photoperiods and light regimes, we further elucidated that the number of cauline branches is closely related to flowering time. The number or rosette branches has an enormous plasticity compared with cauline branches and is influenced by genetic background, flowering time, light intensity and temperature. Our data reveal different plasticity in the regulation of branching at rosette and cauline nodes and promote a framework for future branching analyses.

A Novel DUF569 Gene Is a Positive Regulator of the Drought Stress Response in Arabidopsis

In the last two decades, global environmental change has increased abiotic stress on plants and severely affected crops. For example, drought stress is a serious abiotic stress that rapidly and substantially alters the morphological, physiological, and molecular responses of plants. In Arabidopsis, several drought-responsive genes have been identified; however, the underlying molecular mechanism of drought tolerance in plants remains largely unclear. Here, we report that the “domain of unknown function” novel gene DUF569 (AT1G69890) positively regulates drought stress in Arabidopsis. The Arabidopsis loss-of-function mutant atduf569 showed significant sensitivity to drought stress, i.e., severe wilting at the rosette-leaf stage after water was withheld for 3 days. Importantly, the mutant plant did not recover after rewatering, unlike wild-type (WT) plants. In addition, atduf569 plants showed significantly lower abscisic acid accumulation under optimal and drought-stress conditions, as well as significantly higher electrolyte leakage when compared with WT Col-0 plants. Spectrophotometric analyses also indicated a significantly lower accumulation of polyphenols, flavonoids, carotenoids, and chlorophylls in atduf569 mutant plants. Overall, our results suggest that novel DUF569 is a positive regulator of the response to drought in Arabidopsis.

Genetic analysis of the “head top shape” quality trait of Chinese cabbage and its association with rosette leaf variation

The agricultural and consumer quality of Chinese cabbage is determined by its shape. The shape is defined by the folding of the heading leaves, which defines the head top shape (HTS). The overlapping HTS, in which the heading leaves curve inward and overlap at the top, is the shape preferred by consumers. To understand the genetic regulation of HTS, we generated a large segregating F2 population from a cross between pak choi and Chinese cabbage, with phenotypes ranging from nonheading to heading with either outward curving or inward curving overlapping heading leaves. HTS was correlated with plant height, outer/rosette leaf length, and petiole length. A high-density genetic map was constructed. Quantitative trait locus (QTL) analysis resulted in the identification of 22 QTLs for leafy head-related traits, which included five HTS QTLs. Bulked segregant analysis (BSA) was used to confirm HTS QTLs and identify candidate genes based on informative single-nucleotide polymorphisms. Interestingly, the HTS QTLs colocalized with QTLs for plant height, outer/rosette leaf, and petiole length, consistent with the observed phenotypic correlations. Combined QTL analysis and BSA laid a foundation for molecular marker-assisted breeding of Chinese cabbage HTS and directions for further research on the genetic regulation of this trait.

The pip1s Quintuple Mutants Demonstrate the Essential Roles of PIP1s in the Plant Growth and Development of Arabidopsis

Plasma membrane intrinsic proteins (PIPs) transport water, CO2 and small neutral solutes across the plasma membranes. In this study, we used the clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein 9 system (CRISPR/Cas9) to mutate PIP1;4 and PIP1;5 in a pip1;1,2,3 triple mutant to generate a pip1;1,2,3,4,5 (pip1s−) quintuple mutant. Compared to the wild-type (WT) plant, the pip1s− mutants had smaller sized rosette leaves and flowers, less rosette leaf number, more undeveloped siliques, shorter silique and less seeds. The pollen germination rate of the pip1s− mutant was significantly lower than that of the WT and the outer wall of the pip1s− mutant’s pollen was deformed. The transcriptomic analysis showed significant alterations in the expression of many key genes and transcription factors (TFs) in the pip1s− mutant which involved in the development of leaf, flower and pollen, suggesting that the mutant of PIP1s not only directly affects hydraulics and carbon fixation, but also regulates the expression of related genes to affect plant growth and development.

Natural variation in stress response induced by low CO2 in Arabidopsis thaliana

Variation in atmospheric carbon dioxide (CO2) concentration can dictate plant growth and development and shape plant evolution. For paired populations of 31 Arabidopsis accessions, respectively, grown under 100 or 380 ppm CO2, we compared phenotypic traits related to vegetative growth and flowering time. Four accessions showed the least variation in measured growth traits between 100 ppm CO2 and 380 ppm CO2 conditions, though all accessions exhibited a dwarf stature with reduced biomass under low CO2. Our comparison of accessions also incorporated the altitude (indicated in meters) above sea level at which they were originally collected. Notably, An-1 (50 m), Est (50 m), Ws-0 (150 m), and Ler-0 (600 m) showed the least differences (lower decrease or increase) between treatments in flowering time, rosette leaf number, specific leaf weight, stomatal density, and less negative δ13C values. When variations for all traits and seedset were considered together, Ws-0 exhibited the least change between treatments. Our results showed that physiological and phenotypic responses to low CO2 varied among these accessions and did not correlate linearly with altitude, thus suggesting that slower growth or smaller stature under ambient CO2 may potentially belie a fitness advantage for sustainable growth under low CO2 availability.

Leaf blade anatomy of the rare Siberian flora species Mertensia sibirica (L.) G. Don fil. (Boraginaceae)

The authors present the findings of a leaf blade anatomy study for the rare relict Siberian flora species Mertensia sibirica (L.) G. Don fil. (Boraginaceae). They collected samples for the study from natural habitats in Chita Region (Chikoy Range) and then planted them in the introduction area of the Siberian Botanic Garden (Tomsk) located in the southern taiga subzone of Western Siberia. The parameters of the photosynthetic and stomatal complex of M. sibirica were studied for the first time. It was found out that the rosette and cauline leaves of the species under study are hypostomatous, with an anomocytic stomatal complex. The epidermis is single-layer. On average, the adaxial epidermis has larger cells vs. abaxial epidermis. The leaf mesophyll is 242.90–369.90 µm thick, dorsiventral. The adaxial side of the leaf comprises glandular trichomes surrounded with pronounced rosettes of cells in the base part. The cauline leaf significantly differs from the rosette leaf in finer cells of its adaxial and abaxial epidermis (and, consequently, their larger number per 1 mm2), while the adaxial epidermal cells are thicker, and in a larger number of stomata in the abaxial epidermis. The palisade mesophyll in the cauline leaf is more developed vs. the rosette leaf, while the cells are longer and the palisade/spongy mesophyll ratio is higher. The rosette leaves have a more developed system of vascular tissues vs. cauline ones, as they play the main role in providing plants with water and nutrients. The contribution of the cauline leaf palisade mesophyll to the photosynthetic potential of M. sibirica is higher vs. that of the rosette leaf (the ratio between palisade and spongy mesophyll is 0.45 vs. 0.36, respectively), which characterizes the cauline leaf as more heliophytic. The stomatal complex and mesophyll parameters under study are primarily characterized by low variance. As for dermal tissue parameters, medium variance is typical of the thickness and size of the abaxial and adaxial epidermal cells. Coefficients of variation for the cells of the upper mesophyll layer (CV=31.2–41.6%) and the number of stomata on the lower epidermis of the rosette leaf (CV=21.5%) demonstrate medium and high variance. A very high coefficient of variation (116.2–174.0) is registered for the adaxial epidermis parameter characterizing the density of trichomes per 1 mm2. The study results were used to develop an optimal M. sibirica cultivation regime under conditions of introduction in the southern taiga subzone of Western Siberia.

Proteomic and transcriptomic profiling of aerial organ development in Arabidopsis

Plant growth and development are regulated by a tightly controlled interplay between cell division, cell expansion and cell differentiation during the entire plant life cycle from seed germination to maturity and seed propagation. To explore some of the underlying molecular mechanisms in more detail, we selected different aerial tissue types of the model plant Arabidopsis thaliana, namely rosette leaf, flower and silique/seed and performed proteomic, phosphoproteomic and transcriptomic analyses of sequential growth stages using tandem mass tag-based mass spectrometry and RNA sequencing. With this exploratory multi-omics dataset, development dynamics of photosynthetic tissues can be investigated from different angles. As expected, we found progressive global expression changes between growth stages for all three omics types and often but not always corresponding expression patterns for individual genes on transcript, protein and phosphorylation site level. The biggest difference between proteomic- and transcriptomic-based expression information could be observed for seed samples. Proteomic and transcriptomic data is available via ProteomeXchange and ArrayExpress with the respective identifiers PXD018814 and E-MTAB-7978.

A Sacred Landscape of Sumer: Statuettes from Ur Depicting a Goat on a Tree

The statuettes commonly referred to as “Ram Caught in a Thicket” (2500 BC) may well be associated with what is known from later texts (2nd millennium BC) as the (daily) determining-of-the-fates ritual that occurred at sunrise. Symbolic elements (tree, rosette, leaf, possible mountain), and motifs (quadruped facing a tree) occur in other media—glyptic, musical instruments—and their meaning informs the unique combination of elements found in these two statuettes. It is proposed that the statuettes are offering stands. The composition as a whole represents a sacred landscape rather than a charming genre scene. It is likely that the statuettes were associated with the daily ritual of the determining of the fates, which would push the later attestations of that ritual and the cosmological view behind it back to the mid-third millennium BC.

Gene Expression Changes Occurring at Bolting Time are Associated with Leaf Senescence in Arabidopsis

In plants, the vegetative to reproductive phase transition (termed bolting in Arabidopsis) generally precedes age-dependent leaf senescence (LS). Many studies describe a temporal link between bolting time and LS, as plants that bolt early, senesce early, and plants that bolt late, senesce late. However, the molecular mechanisms underlying this relationship are unknown and are potentially agriculturally important, as they may allow for the development of crops that can overcome early LS caused by stress-related early phase transition. We hypothesized that gene expression changes associated with bolting time were regulating LS. We used a mutant that displays both early bolting and early LS as a model to test this hypothesis. An RNA-seq time series experiment was completed to compare the early bolting mutant to vegetative WT plants of the same age. This allowed us to identify bolting time-associated genes (BAGs) expressed in an older rosette leaf at the time of inflorescence emergence. The BAG list contains many well characterized LS regulators (ORE1, WRKY45, NAP, WRKY28), and GO analysis revealed enrichment for LS and LS-related processes. These bolting associated LS regulators likely contribute to the temporal coupling of bolting time to LS.

Taxonomic revision of the Myosotis australis group (Boraginaceae) native to Australia, New Zealand and New Guinea

The three main aims of this study were to circumscribe the Myosotis australis R.Br. group, determine the taxonomic utility of pollen characters, and delimit species and revise their taxonomy using macro-morphological and palynological data. The M. australis group is here recircumscribed to comprise two species, M. saxatilis Petrie (Marlborough and Otago, New Zealand) and M. australis. Myosotis australis is a widespread, morphologically variable species with two subspecies. M. australis subsp. australis comprises all Australian and most New Zealand specimens, including M. mooreana Lehnebach, M. lytteltonensis (Laing & A.Wall) de Lange, and several white- or yellow-flowered tag-named taxa from New Zealand, whereas M. australis subsp. saruwagedica (Schltr. ex Brand) Meudt, Thorsen & Prebble, comb. et stat. nov. is endemic to New Guinea. The M. australis group can be distinguished from all other ebracteate-erect Myosotis plants sampled to date, including the Australian endemic, M. exarrhena F.Muell., by a suite of characters, i.e. included anthers, calyx with both retrorse and hooked trichomes, rosette leaf trichomes retrorse abaxially and oblique to the midrib adaxially, and leaf length:width ratio of >2:1. Other characters can distinguish the group from M. discolor Pers., M. arvensis (L.) Hill, and M. umbrosa Meudt, Prebble & Thorsen respectively. Pollen characters were not useful for species delimitation within the M. australis group, but they can help distinguish several species outside it, including natural hybrids of M. australis and M. exarrhena in Australia. Myosotis australis, M. saxatilis and M. exarrhena are included in the taxonomic treatment, whereas introduced species M. discolor and M. arvensis are included in the key only.