Grain amaranth genes coding for an RNA-binding and a small, unknown function protein, respectively, enhance thermotolerance when overexpressed in Arabidopsis thaliana

Abstract Recent findings suggest that unknown function genes may contribute to grain amaranths’ capacity to thrive under stressful conditions. In the present study, the overexpression of two grain amaranth unknown function genes, i.e., AhHAB4-PAI-1 and Ah2880 , in Arabidopsis thaliana supported this premise by enhancing their thermotolerance. These genes were identified in stress-exposed Amaranthus hypochondriacus plants and were also induced by heat shock (HS) conditions. Accordingly, both transgenic A. thaliana lines recovered from HS exposure that was near-lethal to untransformed plants. Transcriptional and microscopic analyses indicated that enhanced HS tolerance in both transgenic plant lines occurred by yet to be defined mechanisms that followed strikingly different time-course activation patterns, as evinced by: (i) the accumulation of RNA florescence signals, hypothetically representative of stress granules, which reached their highest intensity in the midst of HS conditions, in AhHAB4-PAI-1 OE plants, and at the initial recovery phase, in Ah2880 OE plants, and (ii) the analysis of transcriptomic data, which revealed a clear difference in the nature, timing and abundance of differentially expressed genes (DEGs) recorded in both OE plants during the HS and recovery stages. Collectively, most DEGs were representative of known heat stress-related responses, predominantly DNA repair, alternative splicing, chromatin remodeling, protein stabilization/degradation/modification, autophagy, cell wall and membrane alterations, ribosomal and organellar responses, high molecular weight complex formation and activation of stress-associated transcription factors and phytohormone signaling. This study’s results highlight the potential use of unknown function genes for the generation of highly heat stress-resistant plants, which may occur through contrasting protective mechanisms.