Paxillin is a prominent focal adhesion docking protein that regulates cell adhesion and migration. Although numerous paxillin-binding proteins have been identified and paxillin is required for normal embryogenesis, the precise mechanism by which paxillin functions in vivo has not yet been determined. We identified an ortholog of mammalian paxillin in Drosophila (Dpax) and have undertaken a genetic analysis of paxillin function during development. Overexpression of Dpax disrupted leg and wing development, suggesting a role for paxillin in imaginal disc morphogenesis. These defects may reflect a function for paxillin in regulation of Rho family GTPase signaling as paxillin interacts genetically with Rac and Rho in the developing eye. Moreover, a gain-of-function suppressor screen identified a genetic interaction between Dpax and cdi in wing development. cdi belongs to the cofilin kinase family, which includes the downstream Rho target, LIM kinase (LIMK). Significantly, strong genetic interactions were detected between Dpax and Dlimk, as well as downstream effectors of Dlimk. Supporting these genetic data, biochemical studies indicate that paxillin regulates Rac and Rho activity, positively regulating Rac and negatively regulating Rho. Taken together, these data indicate the importance of paxillin modulation of Rho family GTPases during development and identify the LIMK pathway as a critical target of paxillin-mediated Rho regulation.

Perennial grasses can sequester soil organic carbon (SOC) in sustainably managed biofuel systems, directly mitigating atmospheric CO 2 concentrations while simultaneously generating biomass for renewable energy. The objective of this study was to quantify SOC accumulation and identify the primary drivers of belowground C dynamics in a zero-tillage production system of tropical perennial C4 grasses grown for biofuel feedstock in Hawaii. Specifically, the quantity, quality, and fate of soil C inputs were determined for eight grass accessions -four varieties each of napiergrass and Guinea grass. Carbon fluxes (soil CO 2 efflux, aboveground net primary productivity, litterfall, total belowground carbon flux, root decay constant), C pools (SOC pool and root biomass), and C quality (root chemistry, C and nitrogen concentrations, and ratios) were measured through three harvest cycles following conversion of a fallow field to cultivated perennial grasses. A wide range of SOC accumulation occurred, with both significant species and accession effects. Aboveground biomass yield was greater and root lignin concentration was lower for napiergrass than Guinea grass. Structural equation modeling revealed that root lignin concentration was the most important driver of SOC pool: varieties with low root lignin concentration, which was significantly related to rapid root decomposition, accumulated the greatest amount of SOC. Roots with low lignin concentration decomposed rapidly, but the residue and associated microbial biomass/byproducts accumulated as SOC. In general, napiergrass was better suited for promoting soil C sequestration in this system. Further, high yielding varieties with low root lignin concentration provided the greatest climate change mitigation potential in a ratoon system. Understanding the factors affecting SOC accumulation and the net greenhouse gas tradeoffs within a biofuel production system will aid in crop selection to meet multiple goals towards environmental and economic sustainability.

Napier grass is a perennial, tropical C-4 grass that can produce large amounts of forage. However, low temperatures and drought stress limit its productivity and nutritive value as a forage. To overcome these limitations, pearl millet × napier grass hybrids (PMN) were developed. It was hypothesized that PMN hybrids were more drought-tolerant, produced higher yields, and had higher nutritive value than napier grass varieties. The yield and nutritive value of 4 napier grass varieties (Bana grass, Mott, MB4 and N51) and 4 PMN hybrids (PMN2, PMN3, 5344 and 4604) were determined with or without irrigation in a strip plot design in Hawaii. Hybrid PMN3 outperformed napier grass varieties and the other hybrids for yield, while 5344 showed higher nutritional content and digestibility than most other grasses. Dry matter yields during the 110-day study period ranged from 10.3 to 32.1 t/ha without irrigation and 19.6 to 55.8 t/ha with irrigation, indicating that moisture stress was limiting performance in raingrown pastures. Only hybrids PMN3 and PMN2 and variety MB4 showed significant growth responses to irrigation. Further work is needed to evaluate the hybrids in a range of environments over much longer periods to determine if these preliminary results can be reproduced over the long term. Similarly, feeding studies with animals are needed to determine if the in vitro data for digestibility are reflected in superior performance for the promising hybrids.Keywords: Biomass, cattle, in vitro digestion, nutrient content, Pennisetum, tropical grasses. ResumenPasto elefante (Pennisetum purpureum) es una gramínea tropical C-4 que puede producir grandes cantidades de forraje. Sin embargo, temperaturas bajas y sequía limitan su productividad y valor nutritivo. Para superar estas limitaciones, se desarrollaron híbridos P. glaucum (sin. P. americanum) × P. purpureum, bajo la hipótesis que, en comparación con las variedades del pasto elefante, los híbridos son más tolerantes a la sequía y más productivos, y tienen mayor valor nutritivo. En este estudio se determinaron la producción de materia seca (MS) y el valor nutritivo de 4 variedades de pasto elefante (los cultivares Bana, Mott, MB4 y N51) y de 4 híbridos (PMN2, PMN3, 5344 y 4604), con o sin riego, en un diseño de parcelas divididas con tratamiento en franjas (strip plot) en Hawaii, USA. El híbrido PMN3 superó las variedades de pasto elefante y los otros híbridos respecto al rendimiento de MS, mientras que el híbrido 5344 mostró una mayor concentración de nutrientes y una digestibilidad más alta que la mayoría de las otras gramíneas. Las producciones de MS durante los 110 días del estudio oscilaron entre 10.3 y 32.1 t/ha sin riego y entre 19.6 y 55.8 t/ha con riego, lo que indica que la falta de humedad estaba limitando el rendimiento. Solo los híbridos PMN3 y PMN2 y la variedad MB4 respondieron al riego con producciones significativamente más altas. Se necesitan más estudios para evaluar los híbridos en una diversidad de ambientes y durante periodos mucho más largos pa...

Napiergrass can produce large amounts of biomass and its nutritive value has a significant effect on its effectiveness for animal production. However, temperature and drought stress limit its productivity. Drought-tolerant pearl millet × napiergrass hybrid (PMN) varieties were developed and produce high biomass yields. The nutritional content and digestibility of PMN is not well known, which limits its use in animal feeding. It was hypothesised that PMN hybrids are more drought tolerant and have higher nutritive value than napiergrass varieties. Four napiergrass varieties (Bana grass, Mott, MB4, and N51) and four PMN (PMN2, PMN3, 5344, 4604) were tested with or without irrigation treatment in a strip-plot design, with the objective of evaluating the nutritional value and in vitro digestibility of PMN hybrids and napiergrass. The forages were harvested on Day 110 of planting. Samples were hand chopped, oven-dried, ground to pass through a 1-mm screen and analysed for their nutrient content and in vitro digestibility using near-infrared spectroscopy. Dry matter (DM) content of PMN2 (24.3%) and PMN3 (22.9%) was significantly higher (P < 0.05) than 5344, Bana grass and N51 napiergrass varieties. No differences (P > 0.05) in acid detergent fibre, neutral detergent fibre, crude protein and metabolisable energy were found among napiergrass varieties. With no effect (P > 0.05) of irrigation, lignin content was highest (P < 0.08) in 4604 (8.2%) and lowest in 5344 (5.2%). Starch was highest (P < 0.05) in irrigated MB4 than both irrigated and non-irrigated 4604. Non-fibre carbohydrate content was highest (P < 0.05) in PMN2 (12.8%) than MB4 (8.7%). The in vitro true digestibility was significantly higher (P < 0.05) in 5344 and Bana grass (70.0% and 68.0% of DM, respectively), than PMN3 (54.5%). Rate of digestion was significantly higher (P < 0.05) in 5344 (4.9%/h) than PMN2 (2.7%/h), others were in between. Neutral detergent fibre digestibility (NDFD) of 5344 and Bana grass (56.7% and 53.2% of neutral detergent fibre, respectively) was significantly higher (P < 0.05) than PMN2 (38.0%). Although no effect of irrigation was observed, there was an interaction (P < 0.05) between variety and irrigation on neutral detergent fibre digestibility of napiergrass varieties. In conclusion, among four PMN varieties tested, PMN3 and 5344 has higher nutritional value and in vitro digestibility than PMN2 and 4604 even when grown in non-irrigated condition. Thus, PMN3 and 5344 is the preferred napiergrass variety for animal feeding, even in rain-fed farming conditions.