Characterization of the Mitochondrial Genome of a Wheat AL-Type Male Sterility Line and the Candidate CMS Gene

Abstract

Heterosis utilization is very important in hybrid seed production. An AL-type cytoplasmic male sterile (CMS) line has been used in wheat-hybrid seed production, but its sterility mechanism has not been explored. In the present study, we sequenced and verified the candidate CMS gene in the AL-type sterile line (AL18A) and its maintainer line (AL18B). In the late uni-nucleate stage, the tapetum cells of AL18A showed delayed programmed cell death (PCD) and termination of microspore at the bi-nucleate stage. As compared to AL18B, the AL18A line produced 100% aborted pollens. The mitochondrial genomes of AL18A and AL18B were sequenced using the next generation sequencing such as Hiseq and PacBio. It was found that the mitochondrial genome of AL18A had 99% similarity with that of Triticum timopheevii, AL18B was identical to that of Triticum aestivum cv. Chinese Yumai. Based on transmembrane structure prediction, 12 orfs were selected as candidate CMS genes, including a previously suggested orf256. Only the lines harboring orf279 showed sterility in the transgenic Arabidopsis system, indicating that orf279 is the CMS gene in the AL-type wheat CMS lines. These results provide a theoretical basis and data support to further analyze the mechanism of AL-type cytoplasmic male sterility in wheat.

Combined Transcriptome and Proteome Analysis of Anthers of AL-type Cytoplasmic Male Sterile Line and Its Maintainer Line Reveals New Insights into Mechanism of Male Sterility in Common Wheat

“…In AL18A anthers, 12 down-regulated and three up-regulated ROS scavenging enzymes were identified at the uni-nuclear stage; whereas, 18 down-regulated and ten up-regulated enzymes were observed at the bi-nucleated stage. These results were consistent with the transcriptome analysis that the redox homeostasis of AL18A is disrupted, which could explain our earlier discovery that AL18A's tapetum PCD was delayed (Hao et al, 2021).…”

“…1504, 916, 2973, and 3889 DEGs between the AL18A and AL18B were obtained at the tetrad, uni-nuclear, bi-nuclear, and the tri-nuclear stages of anther development, respectively (Figure 1B). The number of DEGs gradually increased from the uni-nuclear stage to the tri-nuclear stage, this result is consistent with our previous discovery that AL18A anthers have delayed PCD in the tapetal layer at the uni-nuclear stage (Hao et al, 2021). It is suggested that the early abnormal development of the anther of AL18A was near the uni-nuclear stage.…”

“…This result is consistent with the genetic background of AL18A and AL18B, because they have the same nucleus but different cytoplasm. Combined with our previous studies that orf279 is the CMS gene of AL18A, the first 96 amino acids of ORF279 and ATP8 were identical (Hao et al, 2021), therefore, orf279 may lead to abortion of AL18A by affecting the electron transport chain.…”

“…Previous studies have shown that during anther development, the process of PCD in tapetum is regulated by ROS levels (Yu and Zhang, 2019). Differential expression in the ROS scavenging enzymes suggests changes in ROS levels in the AL18A, this is associated with our previous discovery of delayed PCD in the tapetal cells of AL18A (Hao et al, 2021).…”

“…The DEPs are mainly related to carbohydrate metabolism, energy metabolism, and genetic information processing pathways (Ning et al, 2019). In wheat AL-CMS type sterile line (AL18A), orf279 was reported as the CMS gene (Hao et al, 2021;Melonek et al, 2021), but the sterility mechanism needs further study.…”