MicroRNA miR394 regulates flowering time in Arabidopsis thaliana.

KEY MESSAGE: miR394 regulates Arabidopsis flowering time in a LCR-independent manner. Arabidopsis plants harboring mutations in theMIR394 genes exhibit early flowering, lower expression of floral repressor FLC and higher expression of floral integrators FT and SOC1. Plant development occurs throughout its entire life cycle and involves a phase transition between vegetative and reproductive phases, leading to the flowering process, fruit formation and ultimately seed production. It has been shown that the microRNA394 (miR394) regulates the accumulation of the transcript coding for LEAF CURLING RESPONSIVENESS, a member of a family of F-Box proteins. The miR394 pathway regulates several processes including leaf morphology and development of the shoot apical meristem during embryogenesis, as well as having been assigned a role in the response to biotic and abiotic stress in Arabidopsis thaliana and other species. Here, we characterized plants harboring mutations in MIR394 precursor genes and demonstrate that mir394a mir394b double mutants display an early flowering phenotype which correlates with a lower expression of FLOWERING LOCUS C earlier in development and higher expression of the floral integrators FLOWERING LOCUS T and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1. Consequently, mutant plants produce fewer branches and exhibit lower seed production. Our work reveals previously unknown developmental aspects regulated by the miR394 pathway, in an LCR-independent manner, contributing to the characterization of the multiple roles of this versatile plant regulatory miRNA.

Multiple origins of congested inflorescences in Cyperus s.s. (Cyperaceae): developmental and structural evidence.

PREMISE OF THE STUDY: The understanding of homoplasic structures becomes more relevant when they are complex and define large angiosperm taxa. Inflorescence architecture usually fulfills both features, as happens with Cyperus, a genus with two taxonomical subdivisions characterized either by alternative expressions of Kranz anatomy (C(3) or C(4)) or inflorescence shape (condensed or lax). Those subdivisions are not completely congruent because at least one of these presumed characters has evolved several times. We focused a SEM study on the inflorescence development in species with condensed inflorescences and different photosynthetic anatomy to test the possibility that condensed inflorescences of subgen. Anosporum (C(3) anatomy) have evolved independently from those of subgen. Cyperus (C(4) anatomy). METHODS: Freshly collected inflorescences of C. entrerianus, C. eragrostis, C. oxylepis, and C. incomtus were studied using stereoscopic and scanning electron microscopy. KEY RESULTS: Condensed inflorescences of Cyperus species with C(3) and C(4) anatomy had differences in structure and development: (1) mature structure, (2) position of second-order branching initiation in the first developmental stage of the inflorescence, (3) main axis development and elongation, and branching development, (4) types of ramifications, (5) phyllotaxis and symmetry. CONCLUSIONS: Results support multiple origins of condensed inflorescences in Cyperus, based especially on differences in timing during development and elongation of the main axis and branches, branching pattern and phyllotaxis. Structure and development may be the key to using inflorescence morphology as an external feature to distinguish large natural groups within Cyperus based on vegetative anatomy.

The class I protein AtTCP15 modulates plant development through a pathway that overlaps with the one affected by CIN-like TCP proteins.

The function of the class I TCP transcription factor TCP15 from Arabidopsis thaliana has been studied through the analysis of plants that express a fusion of this protein to the EAR repressor domain. Constitutive expression of TCP15-EAR produces growth arrest at the seedling stage, before leaf emergence. Expression of the repressor fusion from the AtTCP15 promoter produces small plants with leaves whose margins progressively curve upwards, starting from the basal part of the lamina. Leaves contain smaller and less differentiated cells, both on the adaxial and abaxial sides. The abaxial domain is relatively enlarged, with disorganized cells separated by empty spaces. TCP15-EAR also affects the growth of leaf petioles, flower pedicels, and anther filaments. Flowers show reduced elongation of the three outer whorls and altered gynoecia with irregular carpel surfaces and enlarged repla. Ectopic stigma-like structures develop from medial and basal parts of the replum. TCP15-EAR produces an increase in expression of the boundary-specific genes LOB, CUC1, and CUC2. Changes in CUC1 and CUC2 expression can be explained by the existence of lower levels of miR164 in leaves and the repression of IAA3/SHY2 and the SAUR-like gene At1g29460 in leaves and flowers. TCP15 binds to the promoter regions of IAA3/SHY2 and At1g29460, suggesting that these genes may be direct targets of the transcription factor. The results indicate that TCP15 regulates the expression of boundary-specific genes through a pathway that affects auxin homeostasis and partially overlaps with the one modulated by class II CIN-like TCP proteins.

Diversification of inflorescence development in the PCK clade (Poaceae: Panicoideae: Paniceae).

In grasses, inflorescence diversification and its correlation with species evolution are intriguing and not well understood. Part of this problem lies in our lack of comprehension about the inflorescence morphological complexity of grasses. We focused our study on the PCK clade (named for phosphoenol pyruvate carboxykinase), a well-supported monophyletic group for which the relationships among its taxa are not well resolved. Interestingly, the PCK clade has an extensive diversity of adult inflorescence forms. A comparative developmental approach can help us to understand the basis of such morphological differences as well as provide characters that can be used in phylogenetic studies of the group. Using SEM studies, we demonstrate that inflorescence morphology in this clade is even more complex than what is typically observed in adult forms. We describe a number of new characters, and some classical features previously used for taxonomic purposes are redefined on the basis of development. We also define four morphological groups combining adult inflorescence form and development, and we discuss some of the evolutionary aspects of inflorescence diversification in the PCK clade. Taxonomic delimitation among genera in the PCK clade remains confusing and unclear where molecular and morphological studies support different classifications.

Inflorescence, spikelet, and floral development in Panicum maximum and Urochloa plantaginea (Poaceae).

Inflorescence development in Panicum maximum and Urochloa plantaginea was comparatively studied with scanning electron and light microscopy to test the transfer of P. maximum to Urochloa and to look for developmental features applicable to future cladistic studies of the phosphoenol pyruvate carboxykinase (PCK) subtype of C(4) photosynthesis clade (P. maximum and some species of Brachiaria, Chaetium, Eriochloa, Melinis, and Urochloa). Eleven developmental features not discernable in the mature inflorescence were found: direction of branch differentiation; origins of primary branches; apical vs. intercalary development of the main axis; direction of spikelet differentiation; direction of glume, lemma and palea differentiation; position of the lower glume (in some cases); size of the floret meristem; pattern of distal floret development; pattern of gynoecium abortion; differential pollen development between proximal and distal floret; and glume elongation. Inflorescence homologies between P. maximum and U. plantaginea are also clarified. Panicum maximum and U. plantaginea differ not only in their mature inflorescence structure but also in eight fundamental developmental features that exclude P. maximum from Urochloa. The following developmental events are related to sex expression: size of floret meristem, gynoecium abortion, pollen development delay in the proximal floret, glume elongation and basipetal floret maturation at anthesis.

Histopathological Spikelet Changes Produced by Fusarium graminearum in Susceptible and Resistant Wheat Cultivars.

Scab is an important disease of wheat throughout the world. Fusarium graminearum is the species most frequently isolated in Argentina. Histopathological modifications observed in Pro INTA Oasis (a susceptible Argentine cultivar) and in Sumai 3 (a resistant Chinese cultivar) from the time of inoculation, at the spike emergence stage, until major disease expression (10.5 days postinoculation in the susceptible cultivar) are described. Both cultivars showed a horizontal progression of disease, from anthers to glumes, and a vertical progression, from anthers to rachis. Chlorenchyma was the most damaged tissue, with progressive chlorosis and necrosis. Walls of mesophyll, parenchyma, and epidermal cells around the lesions became thicker, particularly in the resistant cultivar. Vessels and sieve tubes were occluded, particularly the former in the susceptible cultivar and the latter in the resistant cultivar. Possible relationships between tissue changes generated during disease progression and known resistance mechanisms are discussed.