CaAP2 transcription factor is a candidate gene for a flowering repressor and a candidate for controlling natural variation of flowering time in Capsicum annuum

Abstract

The APETALA2 transcription factor homolog CaAP2 is a candidate gene for a flowering repressor in pepper, as revealed by induced-mutation phenotype, and a candidate underlying a major QTL controlling natural variation in flowering time. To decipher the genetic control of transition to flowering in pepper (Capsicum spp.) and determine the extent of gene function conservation compared to model species, we isolated and characterized several ethyl methanesulfonate (EMS)-induced mutants that vary in their flowering time compared to the wild type. In the present study, we report on the isolation of an early-flowering mutant that flowers after four leaves on the primary stem compared to nine leaves in the wild-type 'Maor'. By genetic mapping and sequencing of putative candidate genes linked to the mutant phenotype, we identified a member of the APETALA2 (AP2) transcription factor family, CaAP2, which was disrupted in the early-flowering mutant. CaAP2 is a likely ortholog of AP2 that functions as a repressor of flowering in Arabidopsis. To test whether CaAP2 has an effect on controlling natural variation in the transition to flowering in pepper, we performed QTL mapping for flowering time in a cross between early and late-flowering C. annuum accessions. We identified a major QTL in a region of chromosome 2 in which CaAP2 was the most significant marker, explaining 52 % of the phenotypic variation of the trait. Sequence comparison of the CaAP2 open reading frames in the two parents used for QTL mapping did not reveal significant variation. In contrast, significant differences in expression level of CaAP2 were detected between near-isogenic lines that differ for the flowering time QTL, supporting the putative function of CaAP2 as a major repressor of flowering in pepper.

Construction of a high density genetic map of an interspecific cross of Capsicum chinense and Capsicum annuum and QTL analysis of floral traits

“…Strikingly, Capana02g000700 (85140186bp-85144310bp on chromosome 2), which encodes a floral homeotic protein, APETALA 2, was identified. Phylogenetic analysis indicated that the Capana02g000700 homologs from Antirrhinum LIP1 and LIP2 25,26 , Arabidopsis thaliana APETALA2 27 , and pepper CaAP2 28 play an important role in floral development (Fig. 5b).…”

“…Flowering time is a fully quantitative complex trait, and researchers always record the number of days between sowing and anthesis or at certain day after sowing to score the flower or fruit developmental status of the third node to evaluate flowering times 8,15 . In addition, some others also used the leaves numbers on primary stem to evaluate flowering time 28 . After comprehensively comparing the characteristic of parents and progenies used in this and previous studies, we selected the score criterion for evaluating the flowering time, and three QTLs were detected in the study (Table 3).…”

Candidate genes for first flower node identified in pepper using combined SLAF-seq and BSA

“…The transition of the SAM from vegetative to reproductive growth [ 1 , 2 ] reveals its importance in the development of the first flower. In previous studies, FA , CaJ , Ca-ANANTH , Ca-LEAFY , Capsicum annuum S, and CaBLIND were found to promote flower development [ 1 – 5 ], while the CaRNA -binding protein and Ca-APETALA2 were found to suppress flower formation [ 7 , 8 ]. Tan et al (2015) annotated three homologs of Arabidopsis APETALA2 and CLF [ 14 ] as related to leaf number on the primary axis in pepper, which might also be related to FFN.…”

“…The SAM can later undergo a transition to an inflorescence meristem that subsequently develops into the first flower at start of the transition from vegetative to reproductive growth [ 1 , 2 ]. Therefore, the formation of the first flower is a crucial phase in plant growth that is regulated by a complex network of genes that promote [ 1 – 6 ] or suppress [ 7 , 8 ] flowering. The FASCICULATE ( FA ) and CaJOINTLESS ( CaJ ) genes control sympodial shoot development in pepper.…”

“…Additionally, CaJ and CaBLIND are both epistatic to FA for controlling flowering time and suppressing vegetative growth during the reproductive phase of pepper [ 1 , 5 ]. However, the CaRNA -binding protein has a repressive effect on the flowering time [ 8 ], and Ca-APETALA2 , which maps to pepper chromosome 02, represses flowering in pepper [ 7 ]. Although these genes reportedly control the transition from the vegetative stage to the flowering stage during development in pepper, the molecular regulatory mechanisms controlling the formation of the first flower in pepper are still poorly understood.…”