Patterns and drivers of heat production in the plant genus Amorphophallus

Chloroplast genome of four Amorphophallus species: genomic features,comparative analysis, and phylogenetic relationships among Amorphophallus species

BACKGROUND

The genus Amorphophallus (Araceae) contains approximately 250 species, most of which have high ecological and economic significance. The chloroplast genome data and the comprehensive analysis of the chloroplast genome structure of Amorphophallus is limited. In this study, four chloroplast genomes of Amorphophallus were sequenced and assembled. For the first time, comparative analyses of chloroplast genomes were conducted on the 13 Amorphophallus species in conjunction with nine published sequences.

RESULTS

The Amorphophallus chloroplast genomes exhibited typical quadripartite structures with lengths ranging from 164,417 to 177,076 bp. These structures consisted of a large single copy (LSC, 90,705 - 98,561 bp), a small single copy (SSC, 14,172 - 21,575 bp), and a pair of inverted repeats (IRs, 26,225 - 35,204 bp). The genomes contain 108 - 113 unique genes, including 76 - 79 protein-coding genes, 28 - 29 tRNA genes, and 4 rRNA genes. The molecular structure, gene order, content, codon usage, long repeats, and simple sequence repeats (SSRs) within Amorphophallus were generally conserved. However, several variations in intron loss and gene expansion on the IR-SSC boundary regions were found among these 13 genomes. Four mutational hotspot regions, including trnM-atpE, atpB, atpB-rbcL and ycf1 were identified. They could identify and phylogeny future species in the genus Amorphophallus. Positive selection was found for rpl36, ccsA, rpl16, rps4, rps8, rps11, rps12, rps14, clpP, rps3, ycf1, rpl20, rps2, rps18, rps19, atpA, atpF, rpl14, rpoA, rpoC1, rpoC2 and rps15 based on the analyses of Ka/Ks ratios. Phylogenetic inferences based on the complete chloroplast genomes revealed a sister relationship between Amorphophallus and Caladieae. All Amorphophallus species formed a monophyletic evolutionary clade and were divided into three groups, including CA-II, SEA, and CA-I. Amorphophallus albus, A. krausei, A. kachinensis and A. konjac were clustered into the CA-II clade, A. paeoniifolius and A. titanum were clustered into the SEA clade, A. muelleri 'zhuyajin1', Amorphophallus sp, A. coaetaneus, A. tonkinensis and A. yunnanensis were clustered into CA- I clade.

CONCLUSIONS

The genome structure and gene content of Amorphophallus chloroplast genomes are consistent across various species. In this study, the structural variation and comparative genome of chloroplast genomes of Amorphophallus were comprehensively analyzed for the first time. The results provide important genetic information for species classification, identification, molecular breeding, and evolutionary exploration of the genus Amorphophallus.

Molecular basis for thermogenesis and volatile production in the titan arum

The titan arum (Amorphophallus titanum), commonly known as the corpse flower, produces the largest unbranched inflorescence in the world. Its rare blooms last only a few days and are notable both for their burst of thermogenic activity and for the odor of rotting flesh by which they attract pollinators. Studies on the titan arum can therefor lend insight into the mechanisms underlying thermogenesis as well as the production of sulfur-based volatiles, about which little is known in plants. Here, we made use of transcriptome and metabolite analyses to uncover underlying mechanisms that enable thermogenesis and volatile production in the titan arum. The ability to perform thermogenesis correlated with the expression of genes involved in bypass steps for the mitochondrial electron transport chain, in particular alternative oxidase expression, and through our analysis is placed within the context of sugar transport and metabolism. The major odorants produced by the titan arum are dimethyl disulfide and dimethyl trisulfide, and we identified pathways for sulfur transport and metabolism that culminate in the production of methionine, which our analysis identifies as the amino acid substrate for production of these odorants. Putrescine, derived from arginine, was identified as an additional and previously unrecognized component of the titan arum's odor. Levels of free methionine and putrescine were rapidly depleted during thermogenesis, consistent with roles in production of the titan arum's odor. Models for how tissues of the titan arum contribute to thermogenesis and volatile production are proposed.

Floral thermal biology in relation to pollen thermal performance in an early spring flowering plant

The floral microenvironment impacts gametophyte viability and plant-pollinator interactions. Plants employ mechanisms to modify floral temperature, including thermogenesis, absorption of solar radiation, and evaporative cooling. Whether floral thermoregulation impacts reproductive fitness, and how floral morphological variation mediates thermoregulatory capacity are poorly understood. We measured temperature of the floral microenvironment in the field and tested for thermogenesis in the lab in early spring flowering Hexastylis arifolia (Aristolochiaceae). We evaluated whether thermoregulatory capacity was associated with floral morphological variation. Finally, we experimentally determined the thermal optimum and tolerance of pollen to assess whether thermoregulation may ameliorate thermal stress to pollen. Pollen germination was optimal near 21 °C, with a 50% tolerance breadth of ~18 °C. In laboratory conditions, flowers exhibited thermogenesis of 1.5-4.8 °C for short intervals within a conserved timeframe (08:00-09:00 h). In the field, temperature inside the floral tube often deviated from ambient - floral interiors were up to 4 °C above ambient when it was cold, but some fell nearly 10 °C below ambient during peak heat. Flowers with smaller openings were cooler and more thermally stable than those with larger openings during peak heat. Thermoregulation maintained a floral microenvironment within the thermal tolerance breadth of pollen. Results suggest that H. arifolia flowers have a stronger capacity to cool than to warm, and that narrower floral openings create a distinct floral microenvironment, enhancing floral cooling effects. While deviation of floral temperature from ambient conditions maintains a suitable environment for pollen and suggests an adaptive role of thermoregulation, we discuss adaptive and nonadaptive mechanisms underlying floral warming and cooling.

Multifunctionality of angiosperm floral bracts: a review

Floral bracts (bracteoles, cataphylls) are leaf-like organs that subtend flowers or inflorescences but are of non-floral origin; they occur in a wide diversity of species, representing multiple independent origins, and exhibit great variation in form and function. Although much attention has been paid to bracts over the past 150 years, our understanding of their adaptive significance remains remarkably incomplete. This is because most studies of bract function and evolution focus on only one or a few selective factors. It is widely recognised that bracts experience selection mediated by pollinators, particularly for enhancing pollinator attraction through strong visual, olfactory, or echo-acoustic contrast with the background and through signalling the presence of pollinator rewards, either honestly (providing rewards for pollinators), or deceptively (attraction without reward or even trapping pollinators). However, studies in recent decades have demonstrated that bract evolution is also affected by agents other than pollinators. Bracts can protect flowers, fruits, or seeds from herbivores by displaying warning signals, camouflaging conspicuous reproductive organs, or by providing physical barriers or toxic chemicals. Reviews of published studies show that bracts can also promote seed dispersal and ameliorate the effects of abiotic stressors, such as low temperature, strong ultraviolet radiation, heavy rain, drought, and/or mechanical abrasion, on reproductive organs or for the plants' pollinators. In addition, green bracts and greening of colourful bracts after pollination promote photosynthetic activity, providing substantial carbon (photosynthates) for fruit or seed development, especially late in a plant's life cycle or season, when leaves have started to senesce. A further layer of complexity derives from the fact that the agents of selection driving the evolution of bracts vary between species and even between different developmental stages within a species, and selection by one agent can be reinforced or opposed by other agents. In summary, our survey of the literature reveals that bracts are multifunctional and subject to multiple agents of selection. To understand fully the functional and evolutionary significance of bracts, it is necessary to consider multiple selection agents throughout the life of the plant, using integrative approaches to data collection and analysis.

Visual-, Olfactory-, and Nectar-Taste-Based Flower Aposematism

Florivory, i.e., flower herbivory, of various types is common and can strongly reduce plant fitness. Flowers suffer two very different types of herbivory: (1) the classic herbivory of consuming tissues and (2) nectar theft. Unlike the non-reversibility of consumed tissues, nectar theft, while potentially reducing a plant's fitness by lowering its attraction to pollinators, can, in various cases, be fixed quickly by the production of additional nectar. Therefore, various mechanisms to avoid or reduce florivory have evolved. Here, I focus on one of the flowers' defensive mechanisms, aposematism, i.e., warning signaling to avoid or at least reduce herbivory via the repelling of herbivores. While plant aposematism of various types was almost ignored until the year 2000, it is a common anti-herbivory defense mechanism in many plant taxa, operating visually, olfactorily, and, in the case of nectar, via a bitter taste. Flower aposematism has received only very little focused attention as such, and many of the relevant publications that actually demonstrated herbivore repellence and avoidance learning following flower signaling did not refer to repellence as aposematism. Here, I review what is known concerning visual-, olfactory-, and nectar-taste-based flower aposematism, including some relevant cases of mimicry, and suggest some lines for future research.