Morphological analysis and stage determination of anther development in Sorghum [Sorghum bicolor (L.) Moench]

Abstract

Main Conclusion The characteristics of sorghum anthers at 18 classified developmental stages provide an important reference for future studies on sorghum reproductive biology and abiotic stress tolerance of sorghum pollen. Abstract Sorghum (Sorghum bicolor L. Moench) is the fifth-most important cereal crop in the world. It has relatively high resilience to drought and high temperature stresses during vegetative growing stages comparing to other major cereal crops. However, like other cereal crops, the sensitivity of male organ to heat and drought can severely depress sorghum yield due to reduced fertility and pollination efficiency if the stress occurs at the reproductive stage. Identification of the most vulnerable stages and the genes and genetic networks that differentially regulate the abiotic stress responses during anther development are two critical prerequisites for targeted molecular trait selection and for enhanced environmentally resilient sorghum in breeding using a variety of genetic modification strategies. However, in sorghum, anther developmental stages have not been determined. The distinctive cellular characteristics associated with anther development have not been well examined. Lack of such critical information is a major obstacle in the studies of anther and pollen development in sorghum. In this study, we examined the morphological changes of sorghum anthers at cellular level during entire male organ development processes using a modified high-throughput imaging variable pressure scanning electron microscopy and traditional light microscopy methods. We divided sorghum anther development into 18 distinctive stages and provided detailed description of the morphological changes in sorghum anthers for each stage. The findings of this study will serve as an important reference for future studies focusing on sorghum physiology, reproductive biology, genetics, and genomics.

The effects of heat stress on male reproduction and tillering in Sorghum bicolor

“…To investigate what caused pollen sterility under short-term heat stress conditions, we conducted semithin section analysis to examine anther development. In late-stage anthers under normal conditions, we observed uniformly spherical developing pollen grains and a thin layer of heavily stained tapetal cells at stage 10 (Figure 6f; Laza et al, 2022); mature pollen grains formed by stage 13 (Figure 6h). However, the 3-day heat-stressed stage-10 anther exhibited lightly stained hypertrophic tapetal cells (Figure 6g), indicating abnormal differentiation or degeneration in the tapetal cells.…”

“…Sorghum has a similar anther structure to that of maize. Both sorghum and maize anthers comprise four lobes (microsporangia); within each lobe, the central pollen mother cells (PMC) are surrounded by four layers of somatic cells, i.e., the epidermis, endothecium, middle layer, and tapetum (Cheng et al, 1979; Christensen et al, 1972; Laza et al, 2022). Proper development of anther is critical for the production of viable pollen and consequently seeds in sorghum.…”

Basic Helix-Loop-Helix Transcription Factors: Regulators for Plant Growth Development and Abiotic Stress Responses

“…The members of the same subfamily always have similar functions. In flowering plants, the anther is a reproductive organ that is composed of meiocytes and four cell layers: the epidermis, endothecium, middle layer, and tapetum [ 66 ]. The rice bHLH transcription factor in subfamily II, TDR Interacting Protein 2 (TIP2), plays an important role in the formation of the middle layer and tapetum during early anther development through the regulation of Tapetum Degeneration Retardation (TDR) and Eternal Tapetum 1 (EAT1).…”

Responses of sorghum to cold stress: A review focused on molecular breeding

“…It is challenging to determine when and where the sorghum domestication occurred. However, it is assumed that it occurred in Northeastern Africa (Morris et al, 2013) under hot and dry field conditions (Jain et al, 2010;Laza et al, 2022). Sorghum has been well adapted to drought and high-temperature environments where the growth of other cereals crop may be challenged.…”

“…Sorghum is a cold-sensitive crop, but some varieties are cold tolerant (Leon-Velasco et al, 2009;Mansour et al, 2021). Adverse effects in sorghum such as reduction in germination, plant growth, and development are evident by cold stress (Ercoli et al, 2004;Chinnusamy et al, 2007;Janmohammadi et al, 2015;Ortiz et al, 2017;Laza et al, 2022). Integration of signal perception and transduction, gene expression, and molecules produced in response to cold stress is essential to understand sorghum tolerance and acclimatization (Mehrotra et al, 2020).…”