Two duplicate CYP704B1-homologous genes BnMs1 and BnMs2 are required for pollen exine formation and tapetal development in Brassica napus

Abstract

SUMMARYS45A, a double recessive mutant at both the BnMs1 and BnMs2 loci in Brassica napus, produces no pollen in mature anthers and no seeds by self-fertilization. The BnMs1 and BnMs2 genes, which have redundant functions in the control of male fertility, are positioned on linkage groups N7 and N16, respectively, and are located at the same locus on Arabidopsis chromosome 1 based on collinearity between Arabidopsis and Brassica. Complementation tests indicated that one candidate gene, BnCYP704B1, a member of the cytochrome P450 family, can rescue male sterility. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of the developing anther showed that pollen-wall formation in the mutant was severely compromised, with a lack of sporopollenin or exine. The phenotype was first evident at the tetrad stage (stage 7) of anther development, coinciding with the maximum BnCYP704B1 mRNA accumulation observed in tapetal cells at stages 7-8 (haploid stage). TEM also suggested that development of the tapetum was seriously defective due to the disturbed lipid metabolism in the S45A mutant. A TUNEL assay indicated that the pattern of programmed cell death in the tapetum of the S45A mutant was defective. Lipid analysis showed that the total fatty acid content was reduced in the S45A mutant, indicating that BnCYP704B1 is involved in lipid metabolism. These data suggest that BnCYP704B1 participates in a vital tapetum-specific metabolic pathway that is not only involved in exine formation but is also required for basic tapetal cell development and function.

Male Sterile2 Encodes a Plastid-Localized Fatty Acyl Carrier Protein Reductase Required for Pollen Exine Development in Arabidopsis

“…3) that is consistent with the tapetal role in synthesizing and secreting lipidic sporopollenin precursors . This expression pattern is similar to other tapetumexpressed genes, such as the fatty acid-metabolizing genes CYP703s (Morant et al, 2007;Aya et al, 2009), ACOS5 (de Azevedo Souza et al, 2009), CYP704Bs (Dobritsa et al, 2009;Yi et al, 2010), TKPR1/2 (Grienenberger et al, 2010), and LAP6/PKSA and LAP5/PKSB (Tang et al, 2009;Dobritsa et al, 2010;Kim et al, 2010b) as well as WBC27/ABCG26 (Quilichini et al, 2010;Xu et al, 2010;Choi et al, 2011;Dou et al, 2011), OsC6 , and DPW (Shi et al, 2011).…”

Defective Pollen WallIs Required for Anther and Microspore Development in Rice and Encodes a Fatty Acyl Carrier Protein Reductase

“…Biosynthesis of fatty acid derivatives is required for reproductive development and fertility in higher plants, as supported by studies of wheat TAA1c (Wang et al, 2002), rice TDR (Li et al, 2006;Zhang et al, 2008), WDA1 (Jung et al, 2006), CYP703A3 (Aya et al, 2009), and CYP704B2 , and Arabidopsis CER1 (Aarts et al, 1995), MS2 (Aarts et al, 1997), CYP703A2 (Morant et al, 2007), ACOS5 (de Azevedo Souza et al, 2009), CYP704B1 (Dobritsa et al, 2009;Yi et al, 2010), TKPR1/2 (Grienenberger et al, 2010), PKSA/ LAP6, and PKSB/LAP5 (Dobritsa et al, 2010;Kim et al, 2010). Our results show that DPW is able to produce C16:0 alcohol, which is critical for pollen exine development.…”

IRREGULAR POLLEN EXINE1 Is a Novel Factor in Anther Cuticle and Pollen Exine Formation

“…MS26 probably encodes a cytochrome P450 monooxygenase (Djukanovic et al, 2013) that is homologous to CYP704B1 in Arabidopsis (Arabidopsis thaliana), CYP704B2 in rice, and BnMS1 and BnMS2 in Brassica napus, the mutation of which results in defective pollen exine. CYP704B1 and CYP704B2 have a similar function in the v-hydroxylation of C16 and C18 fatty acids (Dobritsa et al, 2009;Li et al, 2010;Yi et al, 2010). The mechanism of anther cuticle and pollen wall development remains largely unknown in maize.…”