Systems analyses of key metabolic modules of floral and extrafloral nectaries of cotton

Abstract

23United States 24 25 Author contributions 26 ECC, CJC, and BJN conceived and planned the study. Sample collection, microscopy, and 27 metabolomic analyses were conducted by ECC, SNM, and NAMF. Additional contributions 28 for microscopic analyses were provided by HTH. RNA preparation was completed by PMK, 29 RR, and CJC. MH processed all RNAseq data and conducted informatics analyses in 30 conjunction with ECC. ECC and BJN wrote the manuscript with feedback from all 31 coauthors. 33One sentence summary 34 The eccrine-based model of nectar synthesis and secretion is conserved in both trichomatic 35 and extrafloral nectaries determined by a system-based comparison of cotton (Gossypium 36 hirsutum) nectaries. 37 Abstract 47 Nectar is a primary reward mediating plant-animal mutualisms to improve plant fitness and 48 reproductive success. In Gossypium hirsutum (cotton), four distinct trichomatic nectaries 49 develop, one floral and three extrafloral. The secreted floral and extrafloral nectars serve 50 different purposes, with the floral nectar attracting bees to promote pollination and the 51 extrafloral nectar attracting predatory insects as a means of indirect resistance from herbivores. 52 Cotton therefore provides an ideal system to contrast mechanisms of nectar production and 53 nectar composition between floral and extrafloral nectaries. Here, we report the transcriptome, 54 ultrastructure, and metabolite spatial distribution using mass spectrometric imaging of the four 55 cotton nectary types throughout development. Additionally, the secreted nectar metabolomes 56 were defined and were jointly composed of 197 analytes, 60 of which were identified. 57 Integration of theses datasets support the coordination of merocrine-based and eccrine-based 58 models of nectar synthesis. The nectary ultrastructure supports the merocrine-based model due 59 to the abundance of rough endoplasmic reticulum positioned parallel to the cell walls and 60 profusion of vesicles fusing to the plasma membranes. The eccrine-based model which consist 61 of a progression from starch synthesis to starch degradation and to sucrose biosynthesis was 62 supported by gene expression data. This demonstrates conservation of the eccrine-based model 63 for the first time in both trichomatic and extrafloral nectaries. Lastly, nectary gene expression 64 data provided evidence to support de novo synthesis of amino acids detected in the secreted 65 nectars.66 67 68 69 130 synthesis to assess for the first time whether this model is conserved among trichomatic and 131 extrafloral nectaries. 132 Results 133 Domesticated Upland cotton, G. hirsutum (TM-1), develops four types of nectaries, 134 three are extrafloral and one is floral, and all consist of multicellular glandular trichomes, 135 specifically called papillae. The three extrafloral nectary types, foliar, bracteal, and 136 circumbracteal, are subcategorized as vegetative or reproductive. The vegetative foliar nectary 137is located on the abaxial surface of the leaf midrib ( Fig. 1A; Fig...

Genetic and evolution analysis of extrafloral nectary in cotton

“…In contrast, identifiable differentiated tissues were not observed in both transverse and longitude sections of nectariless mid-veins ( Figure 2k, i, o and p). We observed that the secretory trichomes are multicellular, capitate trichomes (Figure 2j, n and Figure S2) that are like those in the EFNs of Vicia faba and G. hirsutum (Chatt et al, 2019;Davis et al, 1988). Beneath the epidermis, we observed five layers of small cells with densely stained cytoplasm, which are involved in pre-nectar transport of nectar carbohydrates.…”

“…The sucrose-to-hexose ratio ranges from nearly all sucrose to all hexose, which is very important in plant-mutualist interactions (Roy et al, 2017). A recently study showed that glucose and fructose were the predominant components in G. hirsutum nectars (Chatt et al, 2019). Instead of fructose and glucose, which were not detected, G. arboreum nectar includes concentrated sucrose, supporting that the chemical composition of nectar varies widely between species (Adler, 2009).…”

“…Genetic analysis showed that a pair of recessive genes, located on homologous chromosomes A12 and D12, is responsible for nectary formation in allotetraploid cotton (Hou et al, 2013;Meyer and Meyer, 1961;Waghmare et al, 2005). Very recently, a comprehensive study of key metabolic modules of floral and extrafloral nectaries supports the coordination of merocrine-based and eccrine-based models of nectar synthesis in G. hirsutum (Chatt et al, 2019).…”

Outstanding questions in flower metabolism

“…However, how the remaining classes of compounds are secreted and synthesized still remains elusive. Recent work comparing the metabolomes of floral and extrafloral nectars of cotton supports an eccrine model of secretion where new metabolites are synthesized in the nectary parenchyma and are subsequently secreted by a battery of transporters acting downstream of an H + gradient generated by plasma membrane H + ‐ATPases (Chatt et al ., 2019). Given the abundance of transcripts of the pathways of nitrogen assimilation, such work suggests that the novel synthesis of amino acids may also occur in the nectary cells.…”