Transcriptional trajectories of anther development provide candidates for engineering male fertility in sorghum

Abstract

Sorghum is a self-pollinated crop with multiple economic uses as cereal, forage, and biofuel feedstock. Hybrid breeding is a cornerstone for sorghum improvement strategies that currently relies on cytoplasmic male sterile lines. To engineer genic male sterility, it is imperative to examine the genetic components regulating anther/pollen development in sorghum. To this end, we have performed transcriptomic analysis from three temporal stages of developing anthers that correspond to meiotic, microspore and mature pollen stages. A total of 5286 genes were differentially regulated among the three anther stages with 890 of them exhibiting anther-preferential expression. Differentially expressed genes could be clubbed into seven distinct developmental trajectories using K-means clustering. Pathway mapping revealed that genes involved in cell cycle, DNA repair, regulation of transcription, brassinosteroid and auxin biosynthesis/signalling exhibit peak expression in meiotic anthers, while those regulating abiotic stress, carbohydrate metabolism, and transport were enriched in microspore stage. Conversely, genes associated with protein degradation, post-translational modifications, cell wall biosynthesis/modifications, abscisic acid, ethylene, cytokinin and jasmonic acid biosynthesis/ signalling were highly expressed in mature pollen stage. High concurrence in transcriptional dynamics and cis-regulatory elements of differentially expressed genes in rice and sorghum confirmed conserved developmental pathways regulating anther development across species. Comprehensive literature survey in conjunction with orthology analysis and anther-preferential accumulation enabled shortlisting of 21 prospective candidates for in-depth characterization and engineering male fertility in sorghum. Sorghum, grown widely for food, feed, and forage, is a gluten-free substitute for staple grains, and a promising feedstock for biofuels 1. It exhibits huge phenotypic and morphological diversity in key agronomic traits including photoperiod sensitivity, biomass, grain yield, disease resistance, abiotic stress tolerance etc., with considerable scope for genetic enhancement of cultivated sorghum. However, sorghum is a self-pollinated crop with 75 to 95% rate of self-pollination observed under natural conditions with outcrossing rates varying with panicle type, distance between plants, wind direction, etc 2,3. Therefore, overcoming reproductive constraints is a major challenge to utilize sorghum diversity for breeding programs. Plant breeders have been using cytoplasmic (CMS) and nuclear male sterility (NMS) systems to take advantage of hybrid vigour in many self-pollinated crop species 4. While CMS, caused by specific nuclear and mitochondrial genetic interactions, is maternally inherited; NMS results due to defects in nuclear genes usually inherited as a recessive trait 5. Studies in rice suggest that hybrids produced through NMS give higher yields and germplasm utilization efficiency with better genetic stability under diverse environmental condit...

CRISPR/Cas9‐based discovery of maize transcription factors regulating male sterility and their functional conservation in plants

“…As the GMS genes often show anther‐specific or anther‐preferential expression patterns, it is reasonable to predict GMS genes by using anther transcriptomic analysis (i.e. RNA‐seq or microarray assay) in plants (Dhaka et al ., 2020 ; Ma et al ., 2019 ; Wan et al ., 2019 ; Wan et al ., 2020 ). Furthermore, the reverse genetic strategies (e.g.…”

Genome-Wide Association Study for Biomass Related Traits in a Panel of Sorghum bicolor and S. bicolor × S. halepense Populations

“…Among them, Sobic.009G237900 contains two SNPs with high effects on dry mass yield and encodes a putative plastocyanin; its possible role in photosynthesis might in theory explain its association with DMY, as it is known, for example, that yield can be determined by factors regulating photosynthetic electron transport rate ( Ramamoorthy et al, 2018 ); additional studies are, however, required to investigate this hypothesis. Another SNP with important effect on DMY was Chr8_56708385 which identified a gene (Sobic.008G138100) with no evident connection to biomass, but interestingly it is less than 1.5 kb distant from Sobic.008G138200, the sorghum ortholog of rice MEL2 ( Nonomura et al, 2011 ; Dhaka et al, 2020 ). MEL2 is a RNA-recognition-motif (RRM) protein possessing ankyrin repeats and a RING finger motif involved in germ-cell development and meiosis progression, required for premeiotic G1/S-phase transition ( Nonomura et al, 2011 ); it is not clear, however, whether it is involved in the transition from vegetative to reproductive phase, which could explain its association to maturity and biomass-related traits.…”

Development of sorghum mutant genotypes and analysis of their agro-morphological diversity

“…Pollen grain structure and physiology are genetically regulated, and any abnormal meiotic cycle can cause signi cant changes in pollen properties. Pollen fertility has been con rmed to be reduced after mutagen treatments in sorghum (Dhaka et al, 2020). The pollen sterility percentage was found to be signi cantly lower in the M 3 generation than in the M 2 generation, which explains how the recovery mechanism works between the two generations.…”