Adriano Silvério

New Insights into Aluminum Tolerance in Rice: The ASR5 Protein Binds the STAR1 Promoter and Other Aluminum-Responsive Genes

Aluminum (Al) toxicity in plants is one of the primary constraints in crop production. Al³⁺, the most toxic form of Al, is released into soil under acidic conditions and causes extensive damage to plants, especially in the roots. In rice, Al tolerance requires the ASR5 gene, but the molecular function of ASR5 has remained unknown. Here, we perform genome-wide analyses to identify ASR5-dependent Al-responsive genes in rice. Based on ASR5_RNAi silencing in plants, a global transcriptome analysis identified a total of 961 genes that were responsive to Al treatment in wild-type rice roots. Of these genes, 909 did not respond to Al in the ASR5_RNAi plants, indicating a central role for ASR5 in Al-responsive gene expression. Under normal conditions, without Al treatment, the ASR5_RNAi plants expressed 1.756 genes differentially compared to the wild-type plants, and 446 of these genes responded to Al treatment in the wild-type plants. Chromatin immunoprecipitation followed by deep sequencing identified 104 putative target genes that were directly regulated by ASR5 binding to their promoters, including the STAR1 gene, which encodes an ABC transporter required for Al tolerance. Motif analysis of the binding peak sequences revealed the binding motif for ASR5, which was confirmed via in vitro DNA-binding assays using the STAR1 promoter. These results demonstrate that ASR5 acts as a key transcription factor that is essential for Al-responsive gene expression and Al tolerance in rice.

Evolution of oil-producing trichomes in Sisyrinchium (Iridaceae): insights from the first comprehensive phylogenetic analysis of the genus

BACKGROUND AND AIMS Sisyrinchium (Iridaceae: Iridoideae: Sisyrinchieae) is one of the largest, most widespread and most taxonomically complex genera in Iridaceae, with all species except one native to the American continent. Phylogenetic relationships within the genus were investigated and the evolution of oil-producing structures related to specialized oil-bee pollination examined. METHODS Phylogenetic analyses based on eight molecular markers obtained from 101 Sisyrinchium accessions representing 85 species were conducted in the first extensive phylogenetic analysis of the genus. Total evidence analyses confirmed the monophyly of the genus and retrieved nine major clades weakly connected to the subdivisions previously recognized. The resulting phylogenetic hypothesis was used to reconstruct biogeographical patterns, and to trace the evolutionary origin of glandular trichomes present in the flowers of several species. KEY RESULTS AND CONCLUSIONS Glandular trichomes evolved three times independently in the genus. In two cases, these glandular trichomes are oil-secreting, suggesting that the corresponding flowers might be pollinated by oil-bees. Biogeographical patterns indicate expansions from Central America and the northern Andes to the subandean ranges between Chile and Argentina and to the extended area of the Paraná river basin. The distribution of oil-flower species across the phylogenetic trees suggests that oil-producing trichomes may have played a key role in the diversification of the genus, a hypothesis that requires future testing.

Comparative structure of the pollen in species of Passiflora: insights from the pollen wall and cytoplasm contents

Pollen grains of three Brazilian species of Passiflora (P. elegans, P. suberosa and P. haematostigma) belonging to different subgenera were studied with respect to the wall and cytoplasm. New data were obtained on pollen wall histochemistry, cytoplasm contents and organelle inheritance. The structure of the pollen wall layers differed in all the species; P. elegans shares characters with those found in other species from the same subgenus. The exine foot layer is structured and evident only in P. haematostigma and is not structured in P. elegans. The pollen grains have pollenkitt with lipid components. The cytoplasm of the vegetative cell contains dissolved and non-dissolved polysaccharides. The generative cell contains plastids and mitochondria in all the species analyzed, and consequently has the potential for paternal or biparental extranuclear inheritance. Aspects of the evolution of the characters of the species are discussed in the light of a recent phylogeny of the group, with a focus on the three subgenera.

Floral rewards in the tribe Sisyrinchieae (Iridaceae): oil as an alternative to pollen and nectar?

Iridaceae is one of the few families in which floral oils are produced and collected by pollinators as a resource. Perigonal nectaries and trichomal elaiophores are highly unusual within the tribe Sisyrinchieae. Both structures occur mainly on the staminal column, while they are usually distributed on the tepals in the other tribes of the subfamily Iridoideae. Sisyrinchieae is the largest tribe of Iridaceae present on the American continent, and the diversity observed may be related to the exceptional development of trichomal elaiophores within the genus Sisyrinchium, but knowledge concerning the other types of nuptial glandular structures within the tribe is still limited, preventing us from estimating their implication for species diversity. Structural observations and histochemical tests were performed to identify and characterize glandular structures and pollen rewards within the flowers of the genera Orthrosanthus, Sisyrinchium and Solenomelus. Perigonal nectaries were detected only in Solenomelus segethi, and trichomal elaiophores were characterized only within Sisyrinchium. All species showed large amounts of additional resources available for pollinators in the form of pollenkitt and polysaccharides present in the cytoplasm of the pollen grains. The results are discussed in a phylogenetic context, with regard to pollinators and floral rewards reported for the tribe Sisyrinchieae.

A formação da superfície estigmática em Passiflora elegans (Passifloraceae)

Part of the PhD thesis of the first author. Programa de Pós-Graduação em Botânica, Universidade Federal do Rio Grande do Sul. Universidade Federal do Rio Grande do Sul, Depto. Botânica, Lab. Anatomia Vegetal. Av. Bento Gonçalves 9500, Prédio 43423, s/206, 91501-970, Porto Alegre, RS, Brasil. CNPq Productivity in Research Scholarship recipient. *Corresponding author: jorge.mariath@ufrgs.br Abstract The stigma surface is a complex multicellular structure where the development of the pollen tube begins. This development is necessary for sucess in fertilization and depends on recognition processes that involve the anatomy of the stigma. Passiflora is an economically important genus because of its edible fruits. Many authors have described the stigma of Passiflora but nothing is known about the ontogenesis of this structure. This work aimed to describe the formation of the stigmatic surface of Passiflora elegans. Results showed that, in bud, the stigmatic surface of this species is flat with small cells. The cells in the subdermal layer have large vacuoles and the nucleus, near to the external periclinal walls. During its development the stigma surface becomes uneven due to the elongation of cells in the subdermal layer. Elongation results in an increase of external secretory surface area of the stigmas, and probably plays an important role in pollen recognition. The polysaccharide content found in the inner walls of these structures might be involved in the signal process for pollen tube growth during its early development. The morphological evidence presented here shows that, as the stigma of Passiflora is formed by dermal and subdermal cells, it should not be characterized as colleters or papillae and, therefore, it is defined here as stigma emergences. Key-words: anatomy, stigma development, stigma emergence, pollination.A superficie estigmatica e uma estrutura multicelular complexa, onde o tubo polinico inicia o seu desenvolvimento, necessaria para a fecundacao. Este desenvolvimento depende de condicoes favoraveis que envolvem a anatomia do estigma durante o processo de reconhecimento. Passiflora e um genero economicamente importante devido aos seus frutos comestiveis. O estigma de Passiflora tem sido descrito por varios autores, mas o seu processo de formacao e desconhecido. Esse trabalho tem por objetivo descrever o processo de formacao da superficie estigmatica de Passiflora elegans. Os resultados demonstram que durante a fase de botao jovem, a superficie estigmatica e composta por pequenas celulas e apresenta superficie plana. As celulas da camada subdepidermica apresentam grandes vacuolos e nucleo, proximo da parede periclinal externa. Durante o seu desenvolvimento, a superficie estigmatica torna-se irregular devido ao alongamento de celulas da camada subdepidermica. Essas modificacoes resultam em um acrescimo da superficie secretora externa do estigma, e provavelmente desempenham um importante papel no reconhecimento do polen. Os conteudos polissacaridicos encontrados na superficie interna dessas estruturas podem estar envolvidos com os processos de sinalizacao do tubo polinico durante seu desenvolvimento inicial. As evidencias morfologicas observadas nesse trabalho demonstram que as estruturas presentes na superficie do estigma de Passiflora sao constituidas por celulas de origem dermica e subdermica, e nao devem ser caracterizadas como coleteres ou papilas, sendo assim, caracterizadas nesse trabalho como emergencias estigmaticas.

Teaching of Meiosis and Mitosis in Schools of Developing Countries: How to Improve Education with a Plant Reproduction Project

Recent investigations on Biology Education in Brazil showed that most classes involve the use of textbooks and illustrations [1, 2]. Theoretical and lecture classes predominate in Sciences and Biology courses [3, 4], and there is a scarce variety of teaching materials. On the other hand, recent investigations have led to the development of several practical lessons to improve education quality. Some studies involve proposals of biological models [5]; elaboration of teaching games [6]; analysis of biological specimens [7]; laboratory lessons using microscopy [8]; ecotourism in natural ecosystems, observation of wildlife and environment [9] and visits to Natural History Museums, Zoo and Botanical Gardens [3]. Moreover, other initiatives to improve theoretical classes of Biology and Sciences include donation of small libraries to rural public schools [10] and availability of computer with internet access in rooms at schools [11].

Embryology of Flowering Plants Applied to Cytogenetic Studies on Meiosis

The life cycle of plants is constituted by two generations: sporophytic and gametophytic. Gametophytic generation is the sexual generation. Differently from meiosis in animals, which gives rise to gametes, meiosis in plants originates spores. Heterospory occurs in some pterydophytes and in seed plants. This consists of the formation of two types of spores in separate sporangia (androsporangium and gynosporangium). In angiosperms, when meiosis occurs in anther sporangia, the spores are called androspores. When it occurs in seminal rudiment sporangia, they are called gynospores. The sporogenesis develops in a complete endosporic manner. In the case of gynospores formed, generally only one is viable in each sporangium. The viable spore germinates and, after three mitotic divisions, forms the female gametophyte, which develops in the sporangium tissue the nucellus. During the development of the male gametophyte, the first mitosis occurs inside the sporangium, the other ones may occur after male gametophyte release. The androgametophyte is called pollen grain and the gynogametophyte is called embryo sac. The two sperm cells formed in the second mitosis of the male gametophyte, are the male gametes. They are present in the tricellular pollen grain or after mitosis of the generative cells during the pollen tube germination. The female gametes are called egg cell and central cell. In this way, sexual