Drought tolerance in the era of climate change: Are tetraploids the better choice?

Climate change has a significant impact on plant physiology, highlighting the necessity for water conservation and sustainable management practices in horticulture. The most of naturally occurring polyploids are found at the edge of habitat, where conditions are already unfavorable, these plants may be more adapted. However, it is still not clear why tetraploid plants are so superior and what genetic and molecular mechanisms appear in these plants. The aim of this research is to evaluate the genetic diversity, morphological, physiological and gene expression differences between diploid and tetraploid daylilies under drought stress. The methodology of this work was based on diploid and tetraploid daylily plants. Diploid and tetraploid plants were subjected to drought stress where morphophysiological and transcriptome analysis was performed. Overall review of diploid and tetraploid daylilies under severe drought revealed. Tetraploid daylily cultivars are more drought-tolerant than diploid cultivars. Tetraploids tend to hold higher relative water content in leaves, accumulate higher rates of reactive oxygen species, which potentially contribute to defense mechanisms. Diploid plants tend to have two times lower chlorophyll index, photosynthetic pigment changes determining more yellowing foliage with elevated water loss causing early leaf senescence and photosynthetic potential loss. Detailed studies of diploid and autotetraploid Hemerocallis spp. cv. Trahlyta transcriptome analysis reveals significant differences in gene expression patterns and molecular responses to drought stress. Tetraploids activate more signaling pathways (43) than diploids (19) under drought conditions. The most significant among them are phytohormones (abscisic, salicylic and jasmonic acid, auxin, cytokinin and ethylene), MAPK and photosynthesis signaling pathways. In tetraploids, the specific transcription factors - NAC, ERD9 and LOX4 - are activated in response to drought. Combined results show that tetraploid plants were more resistant to drought stress than diploids by activating alternative molecular pathways responsible for adaptation to drought stress.