RNA-Seq analysis unveils gene regulation of fruit size cooperatively determined by velocity and duration of fruit swelling in peach.

Fruit swelling determines fruit size and usually occurs in two distinct time periods in peach. However, little is known about the gene regulation of fruit swelling. In this study, measurements of longitudinal and transverse diameters in developing and ripening peach fruits unveiled two periods of fruit swelling: the first swelling ends at approximately 65 days after flower blooming (DAFB) and the second swelling starts at approximately 75 DAFB. Comparisons of diameters sizes and development periods among cultivars and accessions revealed a cooperative regulation of swelling velocity and swelling duration, which leads to final determination of fruit size. Furthermore, RNA-sequencing was conducted for fruits at the initial swelling, non-swelling interval between the two swellings (hereafter, 'the interval'), second swelling and ripening stages. A total of 110 and 128 differentially expressed genes were screened from fruits in the first and second swelling, respectively. Besides, the nine most differentially expressed genes located within the reported quantitative trait locations (QTLs) of fruit size in peach were detected in both the first and second swelling stages. Those genes have been reported to be involved in mediating cell size, which indicates the occurrence of both cell proliferation and cell expansion in each of the two major periods of fruit swelling. In addition, a potential gene regulation network is proposed herein and could be used to elucidate the molecular mechanism of peach fruit swellings mediated by multiple key genes.

[Mapping QTLs for horizontal resistance to sheath blight in an elite rice restorer line, Minghui 63].

This study was conducted with a recombinant inbred line (RILs) population consisting of 240 recombination lines, derived from an elite combination, Zhenshan 97B x Minghui 63. The RILs and their parents were grown in a randomized complete design with two replications in the years of 1999 and 2000. Sheath blight response ratings for the population and their parents were identified by an improved method of inoculation, which was carried out with short woody toothpicks incubated with a Rhizoctonia solani strain, RH-9, and inserted the third sheath in the late tillering/green ring stage of growth. A linkage map was constructed from the RILs. The QTL mapping of sheath blight resistance was carried out by the method of interval QTL mapping. Two QTLs for sheath blight resistance were detected in each year, and were located on chromosome 5 and chromosome 9, respectively. The QTL for sheath blight resistance on chromosome 5 was flanked by markers C624 and C246 on the basis of 1999 data, and by markers C246 and RM26 using 2000 data. The 1-LOD-confidence intervals of QTLs for sheath blight resistance on chromosome 5 detected in two years greatly overlapped with each other, and the peak of the 1-LOD-confidence intervals were approximately the same site. This suggested that the QTL for resistance on chromosome 5 detected in 1999 was probably the same as the QTL detected in 2000. The QTL for sheath blight resistance on chromosome 9 was located on the marker interval of C472-R2638 in term of 1999 data, and on the interval of RM257-RM242 based on 2000 data, and the two intervals were 9.7 cM away from each other. Based on the effect analysis of QTLs for resistance, the genotype of MH63 had negative additive effects or reduced sheath blight rating.