Maize MS2 encodes an ATP-binding cassette transporter that is essential for anther development

ATP-Binding Cassette G Transporters and Their Multiple Roles Especially for Male Fertility in Arabidopsis, Rice and Maize

“…Subgroup 1 contains 90 half-size ABCGs, including 31 in maize, 31 in rice and 28 in Arabidopsis , which can be further classified into five clades (Clades 1-1 to 1-5). Among them, some ABCGs have been reported to be involved in anther and pollen development, such as AtABCG9 [ 11 ], AtABCG26 [ 12 , 13 , 14 ], OsABCG15 [ 15 , 16 ] and ZmABCG27 (ZmMS2) [ 8 , 10 ] in Clade 1-1, AtABCG11 [ 17 ], OsABCG26 [ 18 , 19 ], ZmABCG13 (ZmMS13) [ 7 ] in Clade 1-2, AtABCG1/16 [ 20 , 21 , 22 ], and OsABCG3 [ 23 , 24 ] in Clade 1-4. Notably, the ABCGs in Clade 1-4 can be classified into two subclades of monocots and dicots, indicating that diversification of these ABCG members is later than that between monocots and dicots during plant evolution.…”

“…Subgroup 2 consists of 58 full-size ABCGs, including 20 in maize, 23 in rice and 15 in Arabidopsis , which can be further classified into three clades (Clades 2-1 to 2-3). Considering that some of the ABCGs have been functionally characterized in Arabidopsis and rice and several maize orthologs of Arabidopsis and rice, known ABCGs have been reported to play similar roles during anther development and male fertility, such as the orthologous ZmABCG27 (previously named as ZmMS2/ZmABCG26) [ 8 , 10 ], OsABCG15 [ 15 , 16 ] and AtABCG26 [ 12 , 13 , 14 ], the orthologous ZmABCG13 (previously named as ZmMS13) [ 7 ], OsABCG26 [ 18 , 19 ] and AtABCG11 [ 17 ]. Therefore, the phylogenetic analysis result will provide helpful information in exploring the functions of unknown ABCG genes in maize.…”

“…OsABCG26 and ZmMS13, orthologs of AtABCG11 in rice and maize, are essential for anther cuticle and pollen exine formation, especially for the translocation of the cuticular wax and cutin monomers generated in the tapetum across anther wall layers for anther cuticle formation [ 7 , 18 , 19 ]. AtABCG26 and its orthologs OsABCG15 in rice and ZmMS2 in maize, play similar roles in controlling pollen exine development and male fertility by mainly transferring sporopollenin precursors from the tapetum onto the developing microspore surface, although loss-of-function mutations of OsABCG15 and ZmMs2 also lead to defective anther cuticle formation [ 8 , 10 , 15 , 16 ]. Arabidopsis AtABCG1 and AtABCG16, and their rice ortholog OsABCG3, are required for the transport of nexine and intine precursors for male gametophyte development in the post-meiotic stages, and for pollen tube growth; the atabcg1atabcg16 double mutant and osabcg3 mutant show defective nexine and intine formation, and thus male fertility [ 21 , 22 , 23 , 24 ].…”

“…Multiple studies have shown that some ABCG orthologs of Arabidopsis , rice, and maize play both conserved and divergent roles in regulating anther development and male fertility. For example, ZmABCG27/ZmMS2 and its orthologs OsABCG15 and AtABCG26, are all required for the translocation of sporopollenin lipidic precursors from the tapetum to the locules for pollen exine development in maize, rice, and Arabidopsis [ 8 , 10 , 13 , 14 , 15 , 19 ]. ZmABCG13/ZmMS13 is essential for anther cuticle and pollen exine formation, consistent with its orthologs AtABCG11 and OsABCG26 in Arabidopsis and rice [ 7 , 17 , 19 ].…”

“…It has been reported that 54 ABCG members exist in maize [ 6 ], but only three ABCG transporters (ZmMS2/ZmABCG26, ZmMS13 and ZmGL13) have been characterized and reported to be required for male fertility or leaf cuticle formation in maize [ 7 , 8 , 9 , 10 ]. Notably, the current nomenclature of the maize ABCG subfamily does not comply with the standard naming system used in Arabidopsis and rice [ 3 , 6 ], and thus results in a lot of inconveniences and problems in maize ABCG research.…”