Gene and protein expression profiling analysis of young spike development in large spike wheat germplasms

The wheat grain number per spike (GNPS) is a major yield-limiting factor in wheat-breeding programs. Germplasms with a high GNPS are therefore valuable for increasing wheat yield potential. To investigate the molecular characteristics of young spike development in large-spike wheat germplasms with high GNPS, we performed gene and protein expression profiling analysis with three high-GNPS wheat lines (Pubing 3228, Pubing 3504 and 4844-12) and one low-GNPS control variety (Fukuho). The phenotypic data for the spikes in two growth seasons showed that the GNPS of the three large-spike wheat lines were significantly higher than that of the Fukuho control line. The Affymetrix wheat chip and isobaric tags for relative and absolute quantitation-tandam mass spectrometry (iTRAQ-MS/MS) technology were employed for gene and protein expression profiling analyses of young spike development, respectively, at the floret primordia differentiation stage. A total of 598 differentially expressed transcripts (270 up-regulated and 328 down-regulated) and 280 proteins (122 up-regulated and 158 down-regulated) were identified in the three high-GNPS lines compared with the control line. We found that the expression of some floral development-related genes, including Wknox1b, the AP2 domain protein kinase and the transcription factor HUA2, were up-regulated in the high-GNPS lines. The expression of the SHEPHERD (SHD) gene was up-regulated at both the transcript and protein levels. Overall, these results suggest that multiple regulatory pathways, including the CLAVATA pathway and the meristem-maintaining KNOX protein pathway, take part in the development of the high-GNPS phenotype in our wheat germplasms.