This research reveals that the up-regulated expression of multiple capsaicinoid biosynthetic genes in pericarp tissue leads to the elevation of total capsaicinoid content in chili pepper fruit. Capsaicinoids are health-functional compounds that are produced uniquely in chili pepper fruits. A high capsaicinoid level is one of the major parameters determining the commercial quality and health-promoting properties of chili peppers. To investigate the mechanisms responsible for its high contents, we compared an extremely pungent cultivar 'Trinidad Moruga Scorpion Yellow' (MY) with other cultivars of different pungency levels (Fushimi-amanaga, Takanotsume, Red Habanero). Capsaicinoid concentrations were markedly higher in MY fruit (23.9 mg/g DW) than in other pungent cultivars including 'Red Habanero' (HB) fruit (14.3 mg/g DW). Comparative analysis of MY and HB reveals that both cultivars accumulated similar capsaicinoid concentrations in the placental septum, with that in the HB pericarp (1.8 mg/g DW) being markedly lower than that in the placental septum (69.1 mg/g DW). The capsaicinoid concentration in HB fruit is dependent on the placental septum, as reported in other accessions. Therefore, even though placental septum tissue contains high capsaicinoid concentrations, those in the pericarp and seeds attenuated its total content. In contrast, the MY pericarp exhibited a markedly higher concentration (23.2 mg/g DW). A qRT-PCR analysis revealed that multiple capsaicinoid biosynthetic pathway genes (Pun1, pAMT, KAS, and BCAT) were strongly up-regulated in placental septum of pungent cultivars. The genes were expressed exclusively in the MY pericarp, but were barely detected in the pericarps of other pungent cultivars. Collectively, the present study indicates that the up-regulated expression of these genes not only in placental septum but also in pericarp plays an important role in driving capsaicinoid accumulation in the whole fruit.

Pungency in peppers is due to the presence of the alkaloid capsaicin and its analogues, collectively known as capsaicinoids. These compounds are only produced in the Capsicum genus and function as deterrents to mammals from consuming the pepper fruits. Pungency in pepper is qualitatively controlled by the Pun1 locus, which encodes a putative acyltransferase enzyme. Mutations in the Pun1 gene result in a loss of pungency, and several Pun1 loss-of-function alleles have been identified in sweet peppers to date (pun1 [1][2][3] ). However, variations in pun1 alleles have not been completely elucidated. In the present study, we report a new type of loss-of-function pun1 allele, named pun1 4 , in a Japanese sweet pepper cultivar, 'Nara Murasaki' (C. annuum). Sequence analysis at the Pun1 locus revealed that this type of Pun1 allele is caused by a single adenine nucleotide insertion in the second exon region. This insertion is unique to 'Nara Murasaki' and is not present in wild-type Pun1. This insertion causes a frameshift mutation and a change in the amino acid sequence, resulting in a truncated protein. The results of gene expression analysis indicated that the expression of Pun1 in 'Nara Murasaki' was hardly detectable, while the transcripts of this gene were strongly expressed in a pungent cultivar. In a co-segregation test, the pun1 4 genotype perfectly co-segregated with non-pungency in 103 F 2 population plants of a cross between 'Nara Murasaki' and a pungent cultivar. 'Nara Murasaki' and a DNA marker to distinguish the pun1 4 allele will be informative for understanding the domestication process of sweet peppers.

High temperatures and increasing CO2 concentrations are a major threat to global wheat (Triticum aestivum L.) production, demanding the development of heat‐tolerant wheat cultivars. Plant physiological traits are potential surrogates for evaluating genetic variation for crop stress tolerance. This research evaluated 23 Australian wheat cultivars and two breeding lines for heat‐tolerance by characterising the associated physiological traits. The interactive effects of heat‐stress and elevated CO2 were studied under controlled greenhouse conditions and delayed sowing in the field with exposure to higher temperature. Physiological changes, pollen viability and grain yield were assessed. A significant correlation was observed between physiological and agronomical traits under high temperature at 35°C and elevated CO2 at 800 µl L−1, providing evidence of adaptation to high temperatures in some genotypes. Variation in stomatal conductance, transpiration rate, canopy temperature, leaf chlorophyll and photosynthesis were associated with maintenance of pollen viability and grain yield at high temperatures. Of the genotypes assessed, seven were classified as heat tolerant at both ambient and elevated CO2 and nine were heat susceptible while the remainder showed a variable response to CO2 at high temperatures. Field data confirmed the heat responses of the most heat‐tolerant and susceptible genotypes. The heat tolerant genotypes identified are candidates for further breeding and selection to improve adaptation to a changing climate.