Genome-Wide Association Study of Vascular Bundle-Related Traits in Maize Stalk

The vascular bundle plays an important role in nutrient transportation in plants and exerts great influence on crop yield. Maize is widely used for food, feed, and fuel, producing the largest yield in the world. However, genes and molecular mechanism controlling vascular bundle-related traits in maize have largely remained undiscovered. In this study, a natural population containing 248 diverse maize inbred lines genotyped with high-throughput SNP markers was used for genome-wide association study. The results showed that broad variations existed for the vascular bundle-related traits which are subject to genetic structure and it was suitable for association analysis. In this study, we identified 15, 13, 2, 1, and 5 SNPs significantly associated with number of small vascular bundle, number of large vascular bundle, average area of single small vascular bundle, average area of single large vascular bundle, and cross-sectional area, respectively. The 210 candidate genes in the confidence interval can be classified into ten biological processes, three cellular components, and eight molecular functions. As for the Kyoto Encyclopedia of Genes and Genomes analysis of the candidate genes, a total of six pathways were identified. Finally, we found five genes related to vascular development, three genes related to cell wall, and two genes related to the mechanical strength of the stalk. Our results provide the further understanding of the genetic foundation of vascular bundle-related traits in maize stalk.

Vascular system of the fertile spikelet of Sorghum (Gramineae: Panicoideae)

The vascular system of the sessile, fertile spikelet of Sorghum was reconstructed from serial transverse sections. The vascular system is a composite of the basipetal extensions of the traces from the appendages on the rachilla. The rachilla immediately above the glumes consists of an outer and an inner series of these vascular extensions. The basipetal continuations of the median traces of the sterile and fertile lemmas, and of the traces from the stamens comprise the inner series. The outer series consists of the continuations of the many lodicule traces and of vascular bundles descending from the posterior of the pistil. The component of the vascular system related to the pistil is a plexus of xylem and phloem in the form of a hollow cylinder traversed by a large vascular bundle that is the basipetal continuation of the stylar bundles. Bundles from the anterior of the pistil merge with the hollow cylinder at its anterior. Several collateral bundles from the placenta merge with the hollow cylinder at its posterior. Distal portions of these placental bundles supply the short chalaza of the ovule but do not enter it. The vascular system of the fertile spikelet of Sorghum is typical of the Panicoideae, and is useful in distinguishing the Panicoideae from the other subfamilies of grasses. Key words: Sorghum, spikelet, floret, vascular system.