Genetic and functional characterization of loss of growth superiority of 22-ploid Morus nigra L. (2n = 22x = 308).

Genus Morus is well-known for its wide range of cytotypic variation. However, its influence on plant performance is not emphasized, especially at higher ploidy levels. An integrated approach, including data mining, synthesis, reconstruction of transcriptome datasets, field experiment, multiple trait estimation, and in vitro leaf disc senescence assay, was carried out to assess the adaptive strategies of 22-ploid (2n = 22x = 308) M. nigra L. (MN) in comparison to hexaploid (2n = 6x = 84) M. serrata Roxb. (MS). The data synthesis approach suggested that divergence of 22-ploid MN (~ 2.25 MYA) was linked to the quaternary glacial period and losses in growth superiority compared to other cytotypes (2x, 3x, 4x, and 6x) of the genus Morus. Gene expression analysis revealed that cell expansion (EXP4A), genome maintenance (CRPS, Dnmt, and RAD52.2), photosynthetic machinery (LHCB2.1, PsaD), and leaf senescence-associated (SGR1) genes were upregulated in MN. Besides the extensive ploidy effect and increased water dependence, MN exhibits reduced photosynthetic rate (Pn) and moisture retention capacity (MRC). Further, the intrinsic activity of ROS, enhanced accumulation of starch, ascorbic acid, and phenolic signs of augmented metabolic expenditure in 22-ploid MN over hexaploid MS. Furthermore, MN exhibited greater survival to in vitro stress exposure (nutrient, dehydration, and salinity) than MS. The current findings underscored the interplay among the plant architecture, physiological and metabolic adjustments, gene expression, and stress response. The present study relaying the mechanisms of loss of growth superiority of 22-ploid MN is likely to be the trajectory of resource-efficient adaptation.