Gene coexpression network analysis reveals the role of SRS genes in senescence leaf of maize (Zea mays L.)

Shi-related sequence (SRS) proteins are plant-specific transcription factors that play important roles in developmental processes, including regulating hormone biosynthesis, response or signal transduction. However, systematical analysis of the SRS gene family in maize has not yet been conducted. In this study, 11 SRS genes with 13 transcripts were identified and characterized. The characteristics of the gene family were analysed in terms of phylogenetic relationships, chromosome distribution and gene structure. RNA-sequencing data analysis showed that the expression patterns of SRS genes were quite different from each other in maize, indicating their divergence in function. Interestingly, the GRMZM2G077752 gene is highly expressed in senescent leaves. Using further coexpression network analysis, we determined that the module containing GRMZM2G077752 were over-represented by genes related to abscisic acid (ABA) stimulus and carbohydrate metabolic process. This result indicated that GRMZM2G077752 might perceive ABA signal and cause the activation of carbohydrate remobilization during leaf ageing. This study provides valuable information for understanding the functions of the SRS genes in maize.

Relationship between the morphogenesis of Italian ryegrass cv. 'BRS Ponteio' with forage and seed production / Relação entre as características morfogênicas do azevém anual cv. 'BRS Ponteio' com a produção de forragem e de sementes

This study aims to verify, accurate and precisely, the responses of Italian ryegrass 'BRS Ponteio' cultivar to different frequencies of defoliation for forage production and especially for seed production. For this purpose, a randomized block design experiment with four replications was conducted. Four frequencies of defoliation were applied (zero, one, two, and three) based on the thermal sum, evaluating the rate of leaf appearance (LAR), phyllochron (P), leaf expansion rate (LER), leaf senescence rate (LSR), stems expansion rate (SER), tillering rate (TR), leaf life span (LL), forage production, proportion of leaf blades, stems plus sheaths, senescent material, and inflorescences, as well as seed production. Second defoliation noticeably altered the morphogenic plant responses, reduced expansion rates and leaf appearance, increased rates of tillering and stems expansion. This phenotypic maintained a high seed production and provided a harvest of forage mass 100% higher than the collected mass in the first cutting. Third defoliation led to an increase of 100% of the harvested forage mass; however, it caused drastic and negative changes in the morphogenic characteristics and seed yielding.

O presente estudo teve o objetivo de verificar, de forma precisa e detalhada, as respostas da cultivar de azevém anual 'BRS Ponteio', às diferentes frequências de desfolha para a produção de forragem e de sementes. Realizou-se, para tanto, um experimento com delineamento de blocos casualizados com quatro repetições. Foram aplicadas quatro frequências de desfolhas (sem, uma, duas e três) baseando-se no acúmulo térmico, onde se avaliou a taxa de aparecimento de folhas (TApF), o filocrono (F), a taxa de expansão de folhas (TEF), taxa de senescência de folhas (TScF), taxa de expansão dos colmos (TEC), taxa de perfilhamento (TP), duração de vida da folha (DVF), produção de forragem, proporção de lâminas foliares, colmos mais bainhas, material senescente e inflorescências em cada tratamento, bem como a produção de sementes. A segunda desfolha alterou marcadamente as respostas morfogênicas da planta, reduziu as taxas de expansão e aparecimento de folhas e aumentou as taxas de perfilhamento e de expansão do colmo. Esta plasticidade fenotípica manteve a alta produção de sementes da planta e propiciou a colheita de massa de forragem 100% superior à massa colhida no primeiro corte. A terceira desfolha propiciou o aumento de 100% da massa de forragem colhida, todavia, promoveu alterações drásticas e negativas nas características morfogênicas e no rendimento de sementes.

The changes of organelle ultrastructure and Ca2+ homeostasis in maize mesophyll cells during the process of drought-induced leaf senescence

The changes of cell ultra structure as well as Ca2+ homeostasis involved in the drought-induced maize leaf senescence was investigated. Meanwhile, many indicatives of leaf senescence including thiobarbituric acid reactive substance (MDA), electrolyte leakage (EL), and chlorophyll along with soluble proteins were also detected during the process. The Polyethylene glycol6000(PEG6000)-incubated detached leaves showed a slight increase in the MDA content and electrolyte leakage during the first 30 min of our detection, which was corresponded to an unobvious alteration of the cell ultrastructure. Other typical senescence parameters measured in whole leaf exhibited a moderate elevation as well. Thereafter, however, the EL and MDA rose to a large extent, which was correlated with a dramatic damage to the cell ultrastructure with concomitant sharp decrease in the chlorophyll and soluble proteins content. The deposits of calcium antimonite, being an indicator for Ca2+ localization, were observed in the vacuoles as well as intercellular spaces in the leaves grown under normal condition. Nevertheless, after PEG treatment, it was revealed a distinct increment of Ca2+ in the cytoplasm as well as chloroplasts and nuclei. Moreover, with long-lasting treatment of PEG to the detached leaves, the concentration of Ca2+ as described above showed a continuous increment which was consist with the remarked alteration of physiological parameters and severe damage to the ultrastructure of cells, all of which indicated the leaf senescence. Such drought-induced leaf senescence might result from a loss of the cell's capability to extrude Ca2+. All above findings give us a good insight into the important role of Ca2+ homeostasis in the process of leaf senescence accelerated by the drought stress.

Molecular Characterization and Functional Prediction of a Novel Leaf SAG Encoding a CBS-domain-containing Protein from Coleus blumei / 中国生物化学与分子生物学报

Leaf senescence is considered as one of important factors to decrease ornamental values of foliage plants. In the attempt to study and understand the molecular mechanism of leaf senescence, a senescent leaf cDNA library of Coleus blumei was constructed and a small EST library was obtained. According to the sequence of an EST fragment with a cystathionine beta synthase (CBS) domain, a novel leaf senescenceassociated gene (SAG) full-length cDNA encoding a CBS-domain-containing protein, denoted Cbcbs, was rapidly cloned using a strategy of RACE combined with cDNA library. The full length of the Cbcbs gene was 859 bp long (accession No. EF076754) and contained a 609 bp open reading frame (ORF) encoding a 202amino acid protein. One stop codon (TAA) was found in 5' UTR and one possible polyadenylation signal,AATAAA, and a pentanucleotide motif, ATTTA, were found in 3' UTR. The CbCBS contained a predicted mitochondrial targeting peptide in the N-terminal region, two conserved and intact CBS domains, four casein kinase Ⅱ (CK Ⅱ) phosphorylation sites, three protein kinase c (PKC) phosphorylation sites and one tyrosine sulfation (TS) site. Sequence comparisons and phylogenetic analysis showed that CbCBS was a novel senescence or stress-associated protein. The prediction analysis of secondary structure and three dimensional structure of CbCBS suggested that the chief function of the protein was decided by the CBS domain pair. The expression pattern of Cbcbs in leaves was analyzed by RT-PCR. It was demonstrated that Cbcbs gene was a senescence-associated gene (SAG) and expressed in all leaf stages, young stage (Y) being the lowest and terminal senescence stage (S3) being the highest, and was upregulated along with the leaf senescence.Function analysis showed that the mature CbCBS maybe acts as a sensor of cellular energy status and directly or indirectly regulates cellular energy levels to increase ATP content in mitochondria during periods of metabolic stress of senescent leaves.