In order to enhance the accuracy of the relative velocity measurement for the Mars explorer formation flight, we develop a relative velocity measurement method. In this method, the spectrometers at two Mars explorers are adopted to measure the starlight frequency shift and to estimate the velocity with respect to the star. Unfortunately, the instantaneous velocity of star can not be predicted accurately, which results in a large error in the velocity measurement. The difference of these two velocities, which does not include the proper motion of star, is the relative velocity between a pair of Mars explorers at the direction of the star. However, this navigation method can not work alone because of unobservability. To make the navigation system observable and improve the accuracy of both absolute and relative navigation for the Mars explorer formation flight, we combine it with X-ray pulsar navigation and the inter-satellite links, and propose an autonomous integrated navigation method with observability. In this integrated navigation scheme, the extended Kalman filter is adopted to deal with the relative velocity, the inter-satellite links and the pulse time-of-arrival, and estimate the absolute and relative navigation information for the Mars explorer formation flight. The simulation results demonstrate that both absolute and relative navigation accuracy of the proposed method are higher than that of the pulsar navigation, especially the relative one.

Growth-regulating factor (GRF) is a plant-specific transcription factor family, which is involved in nearly all of the central developmental processes in plants. However, little is known about GRF family genes in cultivated sunflower. In this study, 17 GRF genes were identified and characterized from sunflower genome. Their gene structures, conserved motifs, chromosomal distributions and phylogenetic relationships were analyzed. The expression patterns of these genes were detected in various tissues of sunflower inbred line SK02R, which revealed that the 10 seed-specific GRF genes may play important roles during seed development in sunflower. Additionally, transcripts changes of the GRFs under two major abiotic stresses and phytohormones showed that most of the detected GRFs were reduced significantly by GA3 treatment, and other treatments(ABA, NaCl and PEG6000) differently regulated various sunflower growth-regulating factors at different time points. MiR396 target analysis indicated that there may exist a complicated homeostasis between miR396 and its targets GRF and WRKY transcription factor genes in cultivated sunflower. The phylogenetic and expression analyses of the GRF gene family in sunflower would be useful for further cloning and function exploration of the HaGRF genes.

Breeding early-maturing cultivars is one of the most important objectives for pear breeding. Very early-maturing pear provides an excellent parental material for crossing, while the immature embryo and low seed germination of its hybrid progenies often limit the selection and breeding of new early-maturing pear cultivars. In this study, we choose a very early maturing pear cultivar ‘Pearl Pear’ as study object, and investigate the effects of cold stratification, culture medium and seed coat on the germination and growth of early maturing pear seeds. Our results show that cold stratification (4℃) treatment could significantly improve the germination rates of early maturing pear seeds. A 100 days of low temperature pre-treatment and germination on White medium could increase the germination rate up to 84.54%. We also observe that seed coat removal could improve the germination activity of early maturing pear seeds, and middle seed coat removal (MSR) represents an optimal method with its high germination rate and low contamination. The results of our study established an improved protocol for seed germination of early-maturing pear seeds, which will greatly facilitate the breeding of new very early-maturing pear cultivars.