Executive Summary : | Sorghum is a multipurpose crop used for food, fodder, forage and biofuels. It has high resilience to drought and high temperature. However, like other grain crops, the spikes in temperature and drought during gametogenesis and early seed development stages in sorghum pose serious threat to the plant fertility and productivity. Recent studies in rice and maize highlighted small RNAs as key regulators of reproductive stage stress tolerance in grasses due to their ability to rapidly tweak gene expression in a cell/tissue-type-specific manner. These include specialized classes of secondary small interfering RNAs such as phasiRNAs, tasiRNAs and easiRNAs which seem to have evolved in a lineage/specific-specific manner. Due to lack of conservation and distinct sequence features of their precursors, their functions have mostly been elucidated by altering the expression of the genes involved in their biogenesis. By collating the transcriptomic data generated in our lab from anther and pistil development stages and from stress treatments available in the public domain, we have identified 47 small RNA machinery genes out of which three genes, AGO6, AGO18b and DCL5, exhibit preferential/specific accumulation in male meiosis and early seed development in sorghum. These genes also exhibit induction in response to drought stress in both pre-flowering and post flowering stages of two varieties of sorghum. Maize homolog of DCL5 has recently been shown to exhibit temperature-dependent male sterility confirming that our strategy has highlighted important candidates for engineering reproductive stage stress tolerance in sorghum. Our hypothesis is that mutating these genes using CRISPR/Cas technology would severly impact biogenesis of specialized small RNAs involved in male meiosis and/or early seed development especially under high temperature and/or drought conditions. The precise impact on sRNAs would be evaluated by sequencing mRNA, small RNA and degradome population of edited lines with expected phenotype. The outcome of the study will not only provide environment-induced male sterile lines to strengthen the hybrid breeding in sorghum but will also guide future strategies to mitigate impact of climate change on crop productivity under field conditions. |