Cloning of a Zoysia ZjLsL and its overexpression to induce axillary meristem initiation and tiller formation in Arabidopsis and bentgrass

Senescence, dormancy and tillering in perennial C4 grasses

Perennial, temperate, C4 grasses, such as switchgrass and miscanthus have been tabbed as sources of herbaceous biomass for the production of green fuels and chemicals based on a number of positive agronomic traits. Although there is important literature on the management of these species for biomass production on marginal lands, numerous aspects of their biology are as yet unexplored at the molecular level. Perenniality, a key agronomic trait, is a function of plant dormancy and winter survival of the below-ground parts of the plants. These include the crowns, rhizomes and meristems that will produce tillers. Maintaining meristem viability is critical for the continued survival of the plants. Plant tillers emerge from the dormant crown and rhizome meristems at the start of the growing period in the spring, progress through a phase of vegetative growth, followed by flowering and eventually undergo senescence. There is nutrient mobilization from the aerial portions of the plant to the crowns and rhizomes during tiller senescence. Signals arising from the shoots and from the environment can be expected to be integrated as the plants enter into dormancy. Plant senescence and dormancy have been well studied in several dicot species and offer a potential framework to understand these processes in temperate C4 perennial grasses. The availability of latitudinally adapted populations for switchgrass presents an opportunity to dissect molecular mechanisms that can impact senescence, dormancy and winter survival. Given the large increase in genomic and other resources for switchgrass, it is anticipated that projected molecular studies with switchgrass will have a broader impact on related species.

Transcriptome analysis of nodes and buds from high and low tillering switchgrass inbred lines

In the last two decades switchgrass has received increasing attention as a promising bioenergy feedstock. Biomass is the principal trait for improvement in switchgrass breeding programs and tillering is an important component of biomass yield. Switchgrass inbred lines derived from a single parent showing vast variation in tiller number trait was used in this study. Axillary buds, which can develop into tillers, and node tissues, which give rise to axillary buds, were collected from high and low tillering inbred lines growing in field conditions. RNA from buds and nodes from the contrasting inbred lines were used for transcriptome profiling with switchgrass Affymetrix genechips. Nearly 7% of the probesets on the genechip exhibited significant differential expression in these lines. Real-time PCR analysis of 30 genes confirmed the differential expression patterns observed with genechips. Cluster analysis aided in identifying probesets unique to high or low tillering lines as well as those specific to buds or nodes of high tillering lines. Rice orthologs of the switchgrass genes were used for gene ontology (GO) analysis with AgriGO. Enrichment of genes associated with amino acid biosynthesis, lipid transport and vesicular transport were observed in low tillering lines. Enrichment of GOs for translation, RNA binding and gene expression in high tillering lines were indicative of active metabolism associated with rapid growth and development. Identification of different classes of transcription factor genes suggests that regulation of many genes determines the complex process of axillary bud initiation and development. Genes identified in this study will complement the current ongoing efforts in quantitative trait loci mapping of tillering in switchgrass.

New insights into desiccation-associated gene regulation by Lilium longiflorum ASR during pollen maturation and in transgenic Arabidopsis

LLA23, a member of the abscisic acid-, stress-, and ripening-induced (ASR) protein family, was previously isolated from lily (Lilium longiflorum) pollen. The lily ASR is induced through desiccation-associated ABA signaling transduction in the pollen. ASRs are highly hydrophilic and intrinsically unstructured proteins with molecular masses generally less than 18 kDa. LLA23 is abundant in the cytoplasm and nuclei of both vegetative and generative cells of pollen grains. The protein in the nucleus and in the cytoplasm is partly regulated by dehydration. A dual role is proposed for LLA23, as a regulator and a protective molecule, upon exposure to water deficits. This chapter reviews the current state of literature on Asr genes, protein structure, function, and their responses to various stresses. In a study, a genome-wide microarray was used to monitor the expression of LLA23-regulated genes, focusing on the relationship between ASR-, glucose-, and drought-inducible genes, and outlined the difference and cross talk of gene expression among these signaling networks. A strong association was observed in the expression of stress-responsive genes and found 25 genes that respond to all three treatments. Highly inducible genes were also found in each specific stress treatment. Promoter sequence analysis of LLA23-inducible genes enabled us not only to identify possible known cis-acting elements in the promoter regions but also to expect the existence of novel cis-acting elements involved in ASR-responsive gene expression. ASR can be used to improve crops and economically important plants against various environmental stresses.