Allelic Differentiation at the E1/Ghd7 Locus Has Allowed Expansion of Rice Cultivation Area

The photoperiod-insensitivity allele e1 is known to be essential for the extremely low photoperiod sensitivity of rice, and thereby enabled rice cultivation in high latitudes (42–53° north (N)). The E1 locus regulating photoperiod-sensitivity was identified on chromosome 7 using a cross between T65 and its near-isogenic line T65w. Sequence analyses confirmed that the E1 and the Ghd7 are the same locus, and haplotype analysis showed that the e1/ghd7-0a is a pioneer allele that enabled rice production in Hokkaido (42–45° N). Further, we detected two novel alleles, e1-ret/ghd7-0ret and E1-r/Ghd7-r, each harboring mutations in the promoter region. These mutant alleles alter the respective expression profiles, leading to marked alteration of flowering time. Moreover, e1-ret/ghd7-0ret, as well as e1/ghd7-0a, was found to have contributed to the establishment of Hokkaido varieties through the marked reduction effect on photoperiod sensitivity, whereas E1-r/Ghd7-r showed a higher expression than the E1/Ghd7 due to the nucleotide substitutions in the cis elements. The haplotype analysis showed that two photoperiod-insensitivity alleles e1/ghd7-0a and e1-ret/ghd7-0ret, originated independently from two sources. These results indicate that naturally occurring allelic variation at the E1/Ghd7 locus allowed expansion of the rice cultivation area through diversification and fine-tuning of flowering time.

Effect of Ppd-1 genes on durum wheat flowering time and grain filling duration in a wide range of latitudes

SUMMARYUnderstanding the effect of genetic factors controlling flowering time is essential to fine-tune crop development to each target environment and to maximize yield. A set of 35 durum wheat genotypes of spring growth-habit involving different allelic combinations at Ppd-A1 and Ppd-B1 genes was grown for 2 years at four sites at latitudes ranging from 19°N to 41°N. The emergence-flowering period was reduced from north to south. The frequency in the collection of the insensitive allele GS-105 at Ppd-A1 was greater (34%) than that of allele GS-100 (20%). Genotypes that flowered earlier due to the presence of alleles causing photoperiod insensitivity extended their grain-filling period, but less than the shortening in flowering time. The effect of the allele conferring photoperiod sensitivity at Ppd-A1 was stronger than that at Ppd-B1 (Ppd-A1b > Ppd-B1b). The effect of photoperiod insensitivity alleles was classified as GS-100 > GS-105 > Ppd-B1a. The phenotypic expression of alleles conferring photoperiod insensitivity at Ppd-A1 increased at sites with average day length from emergence to flowering lower than 12 h. An interaction effect was found between Ppd-A1 and Ppd-B1. Differences between allelic combinations in flowering time accounted for c. 66% of the variability induced by the genotype effect, with the remaining 34% being explained by genes controlling earliness per se. The shortest flowering time across sites corresponded to the allelic combination GS-100/Ppd-B1a, which reduced flowering time by 11 days irrespective of the Ppd-A1b/Ppd-B1b combination. The current study marks a further step towards elucidation of the phenotypic expression of genes regulating photoperiod sensitivity and their interaction with the environment.