Learning from the desert legume tree, Prosopis cineraria to develop stress-tolerant crops

Plants inhabiting adverse growth conditions compete against stresses by the endogenous regulatory elements viz., promoters and terminators at the ‘right time’ (time-of-stress-act), ‘right place’ (tissue-of-act), and ‘right expression’ (time-of-transcription). Heat stress at the reproductive stage impedes pollen viability and stigma receptiveness, affecting the seed set. Prosopis cineraria, the dominant desert-inhabiting legume tree, is heat- and drought-tolerant. The distribution of heat shock elements in a heat-inducible promoter determines the magnitudes of target gene expression in different tissues/organs. Relative expression of P. cineraria heat shock protein 18.2 (PcHsp18.2) in alternate months of 2021 displayed the highest expression in summer. The flowers collected in June, the hottest month (47 °C) of 2021, exhibited a high expression of PcHsp18.2. The germination of the pollen collected was 80 %, and the trees eventually set seeds. Comprehensive analysis of the promoter (pPcHSP18.2) and terminator (tPchsp18.2) of PcHsp18.2 by expressing the gusA in tobacco exhibited the highest expression under heat stress as similar to the expression of PcHsp18.2 in environmental samples. Ectopic expression of gusA under PcHsp18.2 promoter and terminator resulted in an increased seed set due to the viability of pollen and stigma under heat stress. The gusA expression under PcHsp18.2 promoter and terminator was high-fold in anther compared to the Lat52 and g10 (endogenous genes under its promoter and terminator) genes under heat stress. The expression of genes under strong and balanced endogenous inducible promoter and terminator combinations, as in the desert-growing P. cineraria in transgenic plants, enables the development of resilient crops.