In temperate climates, the prolonged cold temperature of winter serves as a seasonal landmark for winter-annual and biennial plants. In these plants, flowering is blocked before winter. In Arabidopsis thaliana, natural variation in the FRIGIDA (FRI) gene is a major determinate of the rapid-cycling vs. winter-annual flowering habits. In winter-annual accessions of Arabidopsis, FRI activity blocks flowering through the up-regulation of the floral inhibitor FLOWERING LOCUS C (FLC). Most rapid-flowering accessions, in contrast, contain null alleles of FRI. By performing a mutant screen in a winter-annual strain, we have identified a locus, FRIGIDA LIKE 1 (FRL1), that is specifically required for the up-regulation of FLC by FRI. Cloning of FRL1 revealed a gene with a predicted protein sequence that is 23% identical to FRI. Despite sequence similarity, FRI and FRL1 do not have redundant functions. FRI and FRL1 belong to a seven-member gene family in Arabidopsis, and FRI, FRL1, and at least one additional family member, FRIGIDA LIKE 2 (FRL2), are in a clade of this family that is required for the winter-annual habit in Arabidopsis. FLOWERING LOCUS C ͉ vernalization ͉ natural variationT o coordinate reproductive development with seasonal change, many plant species found in temperate climates have evolved a biennial or winter-annual growth habit. The distinguishing feature of this growth habit is an obligate or facultative requirement for vernalization before flowering can occur. Thus flowering in biennials and winter annuals is blocked before winter, and exposure to winter permits flowering the next spring. In Arabidopsis thaliana, there exist both winter-annual and rapid-flowering types (1-4), which flower rapidly without vernalization. The vernalization requirement of naturally occurring winter-annual types is due to the dominant alleles of two genes, FRIGIDA (FRI) and FLOWERING LOCUS C (FLC) (5-7). FLC encodes a MADS-domain-containing transcription factor that acts to delay flowering in a dosage-dependent manner, and FRI is required for high levels of FLC expression (8, 9).Rapid-flowering types contain either null alleles of FRI (1-3) or alleles of FLC that are not up-regulated by FRI (1, 10). However, rapid-flowering types can acquire a winter-annual habit by loss-of-function mutations in any of six genes [LUMI-NIDEPENDENS (LD), FCA, FLOWERING LOCUS D (FLD), FPA, FY, and FVE] that define the autonomous floral-promotion pathway (11). Like FRI, the autonomous-pathway genes also affect flowering time through the regulation of FLC (8,9,12). In rapid-flowering accessions, FLC expression is repressed by the autonomous pathway; consequently, autonomous-pathway mutants have high levels of FLC and are late-flowering. In winter-annual accessions, FRI acts epistatically to the autonomous pathway to up-regulate FLC levels and block flowering. Regardless of whether increased FLC expression is due to FRI or autonomous-pathway mutations, vernalization promotes flowering by causing the epigenetic repression of FLC expression (8, 9)...

Tomato-infecting begomoviruses have been reported throughout Brazil since the introduction of the B biotype of Bemisia tabaci. Here, we report a large scale survey on the distribution and genetic diversity of tomato-infecting begomoviruses. Tomato samples with typical begomovirus symptoms were collected in seven different states, comprising the major tomato growing areas of the country. Viruses were detected by polymerase chain reaction (PCR) using universal primers for the genus Begomovirus. PCR-amplified fragments were cloned and sequenced. Based on sequence comparisons and phylogenetic analyses, at least seven previously undescribed species of begomoviruses were found. Four of the new viruses were found exclusively in the Southeastern states, two exclusively in the Northeastern states, and one was found in both regions. Sequence comparisons reveal strong evidence of recombination among the Brazilian begomoviruses. Together, the results indicate the existence of a high degree of pre-existing genetic diversity among tomato-infecting begomoviruses in Brazil and suggest that these viruses have emerged after being transferred from natural hosts to tomatoes, due to the introduction into Brazil of a novel polyfagous biotype of the whitefly vector.

During a survey conducted in several different regions of Brazil, two unique tospoviruses were isolated and characterized, one from chrysanthemum and the other from zucchini. The chrysanthemum virus displayed a broad host range, whereas the virus from zucchini was restricted mainly to the family Cucurbitaceae. Double-antibody sandwich-enzyme-linked immunosorbent assay and western immunoblot analyses demonstrated that both viruses were serologically distinct from all reported tospovirus species including the recently proposed peanut yellow spot virus and iris yellow spot virus (IYSV) species. The nucleotide sequences of the nucleocapsid (N) genes of both viruses contain 780 nucleotides encoding for deduced proteins of 260 amino acids. The N proteins of these two viruses displayed amino acid sequence similarities with the previously described tospovirus species ranging from 20 to 75%, but they were more closely related to each other (80%). Based on the biological and molecular features, these viruses are proposed as two new tospovirus species, designated chrysanthemum stem necrosis virus (CSNV) and zucchini lethal chlorosis virus (ZLCV). With the identification of CSNV and ZLCV, in addition to tomato spotted wilt virus, groundnut ring spot virus, tomato chlorotic spot virus, and IYSV, Brazil harbors the broadest spectrum of tospovirus species reported.

SummaryRecessive mutations that suppress the late-flowering phenotype conferred by FRIGIDA (FRI) and FLOWERING LOCUS C (FLC) and which also result in serrated leaf morphology were identified in T-DNA and fast-neutron mutant populations. Molecular analysis showed that the mutations are caused by lesions in the gene encoding the large subunit of the nuclear mRNA cap-binding protein, ABH1 (ABA hypersensitive1). The suppression of late flowering is caused by the inability of FRI to increase FLC mRNA levels in the abh1 mutant background. The serrated leaf morphology of abh1 is similar to the serrate (se) mutant and, like abh1, se is also a suppressor of FRI-mediated late flowering although it is a weaker suppressor than abh1. Unlike se, in abh1 the rate of leaf production and the number of juvenile leaves are not altered. The abh1 lesion affects several developmental processes, perhaps because the processing of certain mRNAs in these pathways is more sensitive to loss of cap-binding activity than the majority of cellular mRNAs.

A tospovirus from onion causing a disease known as “sapeca” by growers in Brazil was characterized. Symptoms on onion consisted of numerous eyelike spots on the leaves and flower stalks resulting in flower abortion. Nicotiana benthamiana and N. rustica were the only systemic hosts experimentally found. Double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) experiments demonstrated that this virus was serologically related to iris yellow spot virus (IYSV), a tospovirus recently described in the Netherlands. This virus, from onion, based on an amino acid sequence identity of 90.5% for the N gene protein, is regarded as a strain of IYSV and is designated IYSVBR This 10% divergence in the nucleocapsid protein may represent an adaptation of the virus to distinct ecological niches.