BackgroundSugarcane is one of the major crops worldwide. It is cultivated in over 100 countries on 22 million ha. The complex genetic architecture and the lack of a complete genomic sequence in sugarcane hamper the adoption of molecular approaches to study its physiology and to develop new varieties. Investments on the development of new sugarcane varieties have been made to maximize sucrose yield, a trait dependent on photosynthetic capacity. However, detailed studies on sugarcane leaves are scarce. In this work, we report the first molecular and physiological characterization of events taking place along a leaf developmental gradient in sugarcane.ResultsPhotosynthetic response to CO2 indicated divergence in photosynthetic capacity based on PEPcase activity, corroborated by activity quantification (both in vivo and in vitro) and distinct levels of carbon discrimination on different segments along leaf length. Additionally, leaf segments had contrasting amount of chlorophyll, nitrogen and sugars. RNA-Seq data indicated a plethora of biochemical pathways differentially expressed along the leaf. Some transcription factors families were enriched on each segment and their putative functions corroborate with the distinct developmental stages. Several genes with higher expression in the middle segment, the one with the highest photosynthetic rates, were identified and their role in sugarcane productivity is discussed. Interestingly, sugarcane leaf segments had a different transcriptional behavior compared to previously published data from maize.ConclusionThis is the first report of leaf developmental analysis in sugarcane. Our data on sugarcane is another source of information for further studies aiming to understand and/or improve C4 photosynthesis. The segments used in this work were distinct in their physiological status allowing deeper molecular analysis. Although limited in some aspects, the comparison to maize indicates that all data acquired on one C4 species cannot always be easily extrapolated to other species. However, our data indicates that some transcriptional factors were segment-specific and the sugarcane leaf undergoes through the process of suberizarion, photosynthesis establishment and senescence.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0694-z) contains supplementary material, which is available to authorized users.

Lhcb1-2 from pea was constitutively expressed in transgenic tobacco plants and assessed for functional impact. The successful assembly of the encoded proteins into LHCII trimers was confirmed by electrospray tandem mass spectrometry. Constitutive production of LHCb1-2 led to increased number of thylakoid membranes per chloroplast, increased grana stacking, higher chloroplast numbers per palisade cell and increased photosynthetic capacity at low irradiance, both on a chlorophyll and leaf area basis. The transgenic plants also displayed increased cell volume, larger leaves, higher leaf number per plant at flowering, increased biomass and increased seed weight, when grown under low irradiance levels. Under high irradiance, both transgenic and wild type plants displayed similar photosynthetic rates when tested at 25 degrees C; however, the non-photochemical quenching (NPQ) and qE values increased in the transgenic plants. The exposure of transgenic plants to a photoinhibitory treatment (4 degrees C for 4 h, under continuous illumination) resulted in more detrimental impairment of photosynthesis, since recovery was slower than the non-transgenic plants. These data indicate that constitutive expression of additional Lhcb1-2 transgenes led to a series of changes at all levels of the plant (cellular, leaf and whole organism), and a delay in flowering and senescence. The additional production of the pea protein appears to be accommodated by increasing cellular structures such as the number of thylakoids per chloroplast, organelle volume, organelles per cell, and leaf expansion. The presence of the trimeric pea protein in the tobacco LHCII, however, caused a possible change in the organization of the associated super-complex, that in turn limited photosynthesis at low temperature.

Summary Wood production in fast‐growing Eucalyptus grandis trees is highly dependent on both potassium (K) fertilization and water availability but the molecular processes underlying wood formation in response to the combined effects of these two limiting factors remain unknown. E. grandis trees were submitted to four combinations of K‐fertilization and water supply. Weighted gene co‐expression network analysis and MixOmics‐based co‐regulation networks were used to integrate xylem transcriptome, metabolome and complex wood traits. Functional characterization of a candidate gene was performed in transgenic E. grandis hairy roots. This integrated network‐based approach enabled us to identify meaningful biological processes and regulators impacted by K‐fertilization and/or water limitation. It revealed that modules of co‐regulated genes and metabolites strongly correlated to wood complex traits are in the heart of a complex trade‐off between biomass production and stress responses. Nested in these modules, potential new cell‐wall regulators were identified, as further confirmed by the functional characterization of EgMYB137. These findings provide new insights into the regulatory mechanisms of wood formation under stressful conditions, pointing out both known and new regulators co‐opted by K‐fertilization and/or water limitation that may potentially promote adaptive wood traits.

A method for genetic transformation of germinating seeds and seedlings of Eucalyptus grandis × E. urophyllais described using the sonication-assisted Agrobacterium-mediated transformation (SAAT) system. Seeds germinated for 2 d, and 15-d-old seedlings, sonicated for 30 s, had the highest percentage of β-glucuronidase (GUS) transient expression (21.7 and 37.4%, respectively). Pre-sonication greatly enhanced the efficiency of transformation. The differential transformation of tissues was also investigated, with seeds imbibed for 2 d having over 90% of the blue sectors localised in cotyledons and in the intersection of the hypocotyls and roots, whereas in 5-d-old seedlings, 70% of GUS activity was detected in cotyledons. However, 15–17-d-old seedlings had around 60% of transformed sectors localised in the first pair of leaves. The efficiency of the method was also assessed using a chimeric construct containing the Lhcb1*2 gene of the 28 kDa chlorophyll a/b binding pea protein from the LHCII antenna. Four stable transformants were confirmed by genomic blotting.

Saccharum officinarum bagasse (common name: sugarcane bagasse) and Pennisetum purpureum (also known as Napier grass) are among the most promising feedstocks for bioethanol production in Argentina and Brazil. In this study, both biomasses were assessed before and after acid pretreatment and following hydrolysis with Nasutitermes aquilinus and Cortaritermes fulviceps termite gut digestome. The chemical composition analysis of the biomasses after diluted acid pretreatment showed that the hemicellulose fraction was partially removed. The (hemi) cellulolytic activities were evaluated in bacterial culture supernatants of termite gut homogenates grown in treated and untreated biomasses. In all cases, we detected significantly higher endoglucanase and xylanase activities using pretreated biomasses compared to untreated biomasses, carboxymethylcellulose and xylan. Several protein bands with (hemi) cellulolytic activity were detected in zymograms and two-dimensional gel electrophoresis. Some proteins of these bands or spots were identified as xylanolytic peptides by mass spectrometry. Finally, the diversity of cultured cellulolytic bacterial endosymbionts associated to both Argentinean native termite species was analyzed. This study describes, for the first time, bacterial endosymbionts and endogenous (hemi) cellulases of two Argentinean native termites as well as their potential application in degradation of lignocellulosic biomass for bioethanol production.