OsMTD2‐mediated reactive oxygen species (ROS) balance is essential for intact pollen‐tube elongation in rice

Abstract

SUMMARY The highly specialized haploid male gametophyte—pollen consist of two sperm cells and a large vegetative cell. Successful fertilization requires proper growth timing and rupture of the pollen tube until it delivers sperm cells, which occur immediately after a pollen grain hydrates. Although a tight regulation on polar cell‐wall expansion of the pollen tube is fundamentally important, the underlying molecular mechanism remains largely unknown, especially in crop plants. Here, we characterized the function of male‐gene transfer defective 2 (OsMTD2) gene in rice (Oryza sativa), which belongs to the plant‐specific receptor‐like kinase, the CrRLK1L family. We demonstrated that OsMTD2 is an essential male factor participating in pollen‐tube elongation based on genetic evidence and physiological observations. Because of unavailability of homozygous mutant via conventional methods, we used CRISPR‐Cas9 system to obtain homozygous knockout mutant of OsMTD2. We were able to identify phenotypic changes including male sterility due to early pollen‐tube rupture in the mutant. We observed that the production of reactive oxygen species (ROS) was dramatically reduced in mutants of OsMTD2 pollen grain and tubes with defective pectin distribution. Transcriptome analysis of osmtd2‐2 versus wild‐type anthers revealed that genes involved in defense responses, metabolic alteration, transcriptional and protein modification were highly upregulated in the osmtd2‐2 mutant. Through yeast‐two‐hybrid screening, we found that OsMTD2 kinase interacts with E3 ligase SPL11. Taken together, we propose that OsMTD2 has crucial functions in promoting pollen‐tube elongation through cell‐wall modification, possibly by modulating ROS homeostasis during pollen‐tube growth.

Transcriptome Analysis of Triple Mutant for OsMADS62, OsMADS63, and OsMADS68 Reveals the Downstream Regulatory Mechanism for Pollen Germination in Rice (Oryza sativa)

“…Furthermore, OsMADStri showed abnormal intine and pectin staining, and it could not germinate. This was significantly different with ruptured phenotypes from other male-sterile mutant lines [ 16 , 33 , 34 ]. Most male-sterile mutants have a defect in tapetum by unusual programmed-cell death (PCD), which affects early pollen development consisting of young microspore, vacuolated pollen, and binucleate pollen, particularly pollen outer wall development, and causes problems in the entire pollen grains of the mutants [ 36 , 37 , 38 ].…”

“…In addition, studies on genes that function in the pollen maturation process have many limitations. The mutant that has a defect in pollen maturation and tube germination processes cannot participate in fertilization, so it is impossible to obtain homozygous mutants except by using gene-editing techniques [ 33 , 34 ]. Using the CRISPR-Cas9 system, we simultaneously knocked out three OsMADS ( OsMADS62 , OsMADS63 , OsMADS68 ) highly expressed in mature pollen grains.…”

Receptor for Activated C Kinase1B (OsRACK1B) Impairs Fertility in Rice through NADPH-Dependent H2O2 Signaling Pathway

“…The evidence also suggests that cytosolic calcium concentration plays an important role in modulating the NADPH oxidase activity by binding the EF-hand motifs of the N-terminal region of RBOH [ 16 ]. A tight balance between the dynamic regulation of RBOH proteins and the ROS bursts is shown to be essential for plant growth and development, specifically for pollen development, pollen tube elongation, and cell wall integrity [ 17 , 18 , 19 , 20 , 21 , 22 , 23 ].…”

Systematic Analysis of Tobacco CrRLK1L Family Genes and Functional Identification of NtCrRLK1L47 in Environmental Stresses

“…In Group III, NtCrRLK1L19 was clustered together with AtBUPS1 and AtBUPS2 (Figure 1), and their coding genes were predicted to form the collinear pairs (Figure 2), suggesting that the NtCrRLK1L19 might be the homolog of AtBUPS1 and AtBUPS2. Interestingly, it was indicated that the reactive oxygen species (ROS) served downstream of the BUPS/ANX receptor complex, which might confer stress response complex (Zhang et al, 2020a;Kim et al, 2021). Meanwhile, our results revealed that the promoter of the NtCrRLK1L19 gene contains many stress-response elements, and this gene was proved to be induced by salt stress.…”