Use of marigold and Mexican sunflower to control nematode parasites of tomato in Namibia

Field experiments were conducted in Namibia to study the effect of the French marigold and the Mexican sunflower on parasitic nematodes in tomato. It was hypothesized that these plants could suppress nematode infestation of tomato, as previous research has shown that these plants are nematode-suppressive. A cover cropping and a green manure experiment, in conjunction with tomato resistance to the root-knot nematode, were evaluated. The cover cropping experiment comprised a first season planting density of 0, 40, 50, 60 cm $\times$ two nematode suppressive plants (marigold and sunflower), followed by a test cropping in the second season with a nematode susceptible tomato cultivar. The green manure experiment comprised a four-treatment (0, 50, 100, 150 Kg sunflower green manure/19.25 m\sp2 plot) $\times$ two tomato cultivar (resistant or susceptible to root-knot nematodes) design. Marigold was a host plant for nematodes but sunflower was not. However, neither plant suppressed parasitism of tomato. Green manuring increased tomato plant growth but did not suppress nematodes. The resistant tomato cultivar had a suppressive effect on nematodes. The results have relevance to nematode control in Namibia

Alternative Splicing of Circadian Clock Genes Correlates With Temperature in Field-Grown Sugarcane

Alternative Splicing (AS) is a mechanism that generates different mature transcripts from precursor mRNAs (pre-mRNAs) of the same gene. In plants, a wide range of physiological and metabolic events are related to AS, as well as fast responses to changes in temperature. AS is present in around 60% of intron-containing genes in Arabidopsis, 46% in rice, and 38% in maize and it is widespread among the circadian clock genes. Little is known about how AS influences the circadian clock of C4 plants, like commercial sugarcane, a C4 crop with a complex hybrid genome. This work aims to test if the daily dynamics of AS forms of circadian clock genes are regulated by environmental factors, such as temperature, in the field. A systematic search for AS in five sugarcane clock genes, ScLHY, ScPRR37, ScPRR73, ScPRR95, and ScTOC1 using different organs of sugarcane sampled during winter, with 4 months old plants, and during summer, with 9 months old plants, revealed temperature- and organ-dependent expression of at least one alternatively spliced isoform in all genes. Expression of AS isoforms varied according to the season. Our results suggest that AS events in circadian clock genes are correlated with temperature.</p

Functional analysis of splice variant expression of MADS AFFECTING FLOWERING 2 of Arabidopsis thaliana

The MADS-AFFECTING FLOWERING 2 (MAF2) gene of Arabidopsis thaliana has been characterized as a repressor of flowering. The molecular basis of MAF2 gene function and role of alternative MAF2 transcripts in flowering time modulation is not understood. MAF2 splice variant expression was quantified in cold-acclimated plants by quantitative RT-PCR. Cold influenced the abundance of splice variants and prompted a functional study of splice forms. Individual variants were overexpressed in the Col background and were assayed for their ability to delay flowering. Overexpression of MAF2 variants 2 and 4 had limited effect on flowering time. Overexpression of MAF2 splice variant 1 resulted in early flowering and affected the expression of the endogenous MAF2 gene and its paralogues, confounding functional assessment. In the Ll-2 Arabidopsis accession, a MAF2, MAF3, MAF4 and FLC null line, MAF2 var1 was consistent in its effect on reproductive delay under ambient and reduced temperatures, indicating that it acts as a repressor of flowering

Natural Diversity in Flowering Responses of Arabidopsis thaliana Caused by Variation in a Tandem Gene Array

Tandemly arrayed genes that belong to gene families characterize genomes of many organisms. Gene duplication and subsequent relaxation of selection can lead to the establishment of paralogous cluster members that may evolve along different trajectories. Here, we report on the structural variation in MADS AFFECTING FLOWERING 2 (MAF2) gene, one member of the tandemly duplicated cluster of MADS-box-containing transcription factors in Arabidopsis thaliana. The altered gene structure at the MAF2 locus is present as a moderate-frequency polymorphism in Arabidopsis and leads to the extensive diversity in transcript patterns due to alternative splicing. Rearrangements at the MAF2 locus are associated with an early flowering phenotype in BC5 lines. The lack of suppression of flowering time in a MAF2-insertion line expressing the MAF2-specific artificial miRNA suggests that these MAF2 variants are behaving as loss-of-function alleles. The variation in gene architecture is also associated with segregation distortion, which may have facilitated the spread and the establishment of the corresponding alleles throughout the Eurasian range of the A. thaliana population

HUA2 Caused Natural Variation in Shoot Morphology of A. thaliana

SummaryDifferences in life-history strategy are thought to contribute to adaptation to specific environmental conditions. Among life-history traits in plants, flowering time and shoot morphology are particularly important for reproductive success. Even though flowering time and shoot morphology are linked, the evolutionary changes in the genetic circuitry that simultaneously affects both traits remain obscure. Here, we have identified changes in a putative pre-mRNA processing factor, HUA2, as being responsible for the distinct shoot morphology and flowering behavior in Sy-0, a natural strain of Arabidopsis. HUA2 has previously been shown to positively regulate two MADS box genes affecting flowering time (FLOWERING LOCUS C [FLC]) and floral patterning (AGAMOUS [AG]) [1, 2]. We demonstrate that natural changes in HUA2 activity have opposite effects on its known functions, thus having implications for the coordinate control of induction and maintenance of floral fate. The changes in Sy-0 lead to enhanced FLC expression, resulting in an enlarged basal rosette and aerial rosettes, whereas suppression of AG function favors a reversion of floral meristems from determinate to indeterminate development. Natural variation in HUA2 activity thus coordinates changes in two important life-history traits, flowering time and shoot morphology