Soybean is one of the most important food crops worldwide.  Like other legumes, soybean can form symbiotic relationships with Rhizobium species.  Nitrogen fixation of soybean via its symbiosis with Rhizobium is pivotal for sustainable agriculture.  Type III effectors (T3Es) are essential regulators of the establishment of the symbiosis, and nodule number is a feature of nitrogen-affected nodulation.  However, genes encoding T3Es at quantitative trait loci (QTLs) related to nodulation have rarely been identified. Chromosome segment substitution lines (CSSLs) have a common genetic background but only a few loci with heterogeneous genetic information; thus, they are suitable materials for identifying candidate genes at a target locus.  In this study, a CSSL population was used to identify the QTLs related to nodule number in soybean.  Single nucleotide polymorphism (SNP) markers and candidate genes within the QTLs interval were detected, and it was determined which genes showed differential expression between isolines.  Four candidate genes (GmCDPK28, GmNAC1, GmbHLH, and GmERF5) linked to the SNPs were identified as being related to nodule traits and pivotal processes and pathways involved in symbiosis establishment.  A candidate gene (GmERF5) encoding a transcription factor that may interact directly with the T3E NopAA was identified.  The confirmed CSSLs with important segments and candidate genes identified in this study are valuable resources for further studies on the genetic network and T3Es involved in the signaling pathway that is essential for symbiosis establishment. 

There are 41 members of the CCT (CO, CO-like, and TOC1) domain-containing gene family in rice, which are divided into three subfamilies: COL (CONSTANS-like), CMF (CCT motif family), and PRR (pseudoresponse regulator).  The first flowering gene to be isolated by map-based cloning, Heading date 1 (Hd1), which is the orthologue of CO in rice, belongs to COL.  The central regulator of plant development, Ghd7, belongs to CMF.  The major role in controlling rice distribution to high latitudes, Ghd7.1/PRR37, belongs to PRR.  Both of Hd1, Ghd7 and Ghd7.1 simultaneously control grain number, plant height, and the heading date.  To date, 13 CCT family genes from these three subfamilies have been shown to regulate flowering.  Some of them have pleiotropic effects on grain yield, plant height, and abiotic stresses, and others function as circadian oscillators.  There are two independent photoperiod flowering pathways that are mediated by GI-Hd1-Hd3a/RFT and GI-Ehd1-Hd3a/RFT in rice.  CCT family genes are involved in both pathways.  The latest study reveals that protein interaction between Hd1 and Ghd7 integrates the two pathways.  CCT family genes are rich in natural variation because rice cultivars have been subjected to natural and artificial selection for different day lengths in the process of domestication and improvement.  Alleles of several crucial CCT family genes such as Hd1, Ghd7, and Ghd7.1 exhibit geographic distribution patterns and are highly associated with yield potentials.  In addition, CCT family genes are probably involved in the responses to abiotic stress, which should be emphasized in future work.  In general, CCT family genes play important roles in regulating flowering, plant growth, and grain yield.  The functional identification and elucidation of the molecular mechanisms of CCT family genes would help construct a flowering regulatory network and maximize their contribution to rice production.