The photoperiod response of lowering is critical to the survival and successful reproduction in crops. The Hd6 gene, encoding a protein similar to the Arabidopsis α-subunit of CASEIN KINASE2α （CK2α） has been reported to affect flowering time through the photoperiodic pathway in rice. In this study, the maize ortholog, ZmHd6, has been cloned and its role in the photoperiodic pathway was investigated. ZmHd6 encodes 332 amino acids with six distinct domains： two CK2 active domains, a nuclear localization signal sequence, a N terminal domain, an ATP binding site, and an active site of serine/threonine protein kinase. ZmHd6 was constitutively expressed in the leaves and shoot apical meristem （SAM） with the highest expression in SAMs of plants with seven leaves under long and short day conditions. Delayed flowering time under long day （LD） conditions were observed in ZmHd6 overexpression transgenic Arabidopsis plants compared to the wild type. In transgenic Arabidopsis plants, ZmHd6 was expressed in a circadian oscillatory pattern, TOC1 peak expression was delayed, new GI, CO, and FT expressions reached to peak after 3 h while entering illumination period and oscillatory expression patterns of CO and FT were created during the dark phase. These results suggested that ZmHd6 might negatively regulate flowering time under LD conditions by delaying TOC1 peak expression and disrupting CO and FT expression in transgenic Arabidopsis plants.
KU Li-xia LI Si-yuan CHEN Xiao WU Lian-cheng WANG Xin-tao CHEN Yan-hui
Phosphorus （P） is one of the three primary macronutrients that are required in large amounts for plant growth and development. To better understand molecular mechanism of maize and identify relevant genes in response to phosphorus deficiency, we used Solexa/Illumina＇s digital gene expression （DGE） technology to investigate six genome-wide expression profiles of seedling roots of the low-P tolerant maize inbred line 178. DGE studies were conducted at 6, 24 and 72 h under both phosphorus deficient and sufficient conditions. Approximately 3.93 million raw reads for each sample were sequenced and 6 816 genes exhibited significant levels of differential expressions in at least one of three time points in response to P starvation. The number of genes with increased expression increased over time from 6 to 24 h, whereas genes with decreased expression were more abundant at 72 h, suggesting a gradual response process for P deficiency at different stages. Gene annotations illustrated that most of differentially expressed genes （DEGs） are involved in different cellular and molecular processes such as environmental adaptation and carbohydrate metabolism. The expression of some known genes identified in other plants, such as those involved in root architecture, P metabolism and transport were found to be altered at least two folds, indicating that the mechanisms of molecular and morphological adaptation to P starvation are conserved in plants. This study provides insight into the general molecular mechanisms underlying plant adaptation to low-P stress and thus may facilitate molecular breeding for improving P utilization in maize.
Drought is a major constraint in maize production worldwide. We studied quantitative trait loci （QTL） underlying drought tolerance for maize plants grown in two different environments. Traits investigated included ASI, plant height, grain yield, ear height, and ear setting. A genetic linkage map was constructed with 120 simple sequence repeat （SSR） markers based on an F2 population derived from a cross between D5 （resistant parent） and 7924 （susceptible parent）. Correlation and heritability were calculated. QTLs of these traits were identified by composite interval mapping combined with a linkage map covering 1 790.3 cM. The markers were arranged in ten linkage groups. QTL mapping was made of the mean trait performance of the 180 F2：3 population. The results showed five, five, six, four, and five QTLs for ASI, plant height, grain yield, ear height, and ear setting under full irrigation condition, respectively, and four, seven, six, four, and four QTLs for ASI, plant height, grain yield, ear height, and ear setting under severe late stress conditions, respectively. Especially the four QTLs detected for five traits in 2008 and 2009. The universal QTLs information generated in this study will aid in undertaking an integrated breeding strategy for further genetic studies in drought tolerance improvement in maize.
ZHU Jing-jing WANG Xiao-peng SUN Cui-xia ZHU Xiu-miao LI Meng ZHANG Guo-dong TIAN Yan-chen WANG Ze-li
SAUMZ 1 and SAUMZ 2 are two forage maize varieties reproduced by distant hybridization.In a randomized block experiment,their fresh forage yield and dry matter yield were investigated on the basis of growth period,leaf stage,and effective accumulated temperature.The nutritional components were measured in a near infrared diffuse reflectance spectroscopy.Referring to the concept of forage grading index,a formula was constructed to calculate the total digestible energy.The investigated characters and indexes were adapted to suitable models of growth dynamics.The results showed that these two varieties have strong heterosis in fresh forage yield,dry matter yield,and total digestible energy.Their growth dynamics were adapted to Logistic models described by general equation y=k/（1＋ae-bx）.The forage grading indexes of these two varieties were decreased linearly along with the increasing of their leaf stage.The stopping point of fast growing period of total digestible energy estimated on the basis of leaf stage was suggested to be used as optimal harvesting stage of forage maize.The optimal harvesting stage was estimated to be tasseling stage for SAUMZ 1 and 19.50-leaf stage for SAUMZ 2.
FU Feng-ling GUO Chang-jun TANG Qi-ling LIU Jian LI Wan-chen
