ZmMs30 Encoding a Novel GDSL Lipase Is Essential for Male Fertility and Valuable for Hybrid Breeding in Maize

Abstract

Genic male sterility (GMS) is very useful for hybrid vigor utilization and hybrid seed production. Although a large number of GMS genes have been identified in plants, little is known about the roles of GDSL lipase members in anther and pollen development. Here, we report a maize GMS gene, ZmMs30, which encodes a novel type of GDSL lipase with diverged catalytic residues. Enzyme kinetics and activity assays show that ZmMs30 has lipase activity and prefers to substrates with a short carbon chain. ZmMs30 is specifically expressed in maize anthers during stages 7-9. Loss of ZmMs30 function resulted in defective anther cuticle, irregular foot layer of pollen exine, and complete male sterility. Cytological and lipidomics analyses demonstrate that ZmMs30 is crucial for the aliphatic metabolic pathway required for pollen exine formation and anther cuticle development. Furthermore, we found that male sterility caused by loss of ZmMs30 function was stable in various inbred lines with different genetic background, and that it didn't show any negative effect on maize heterosis and production, suggesting that ZmMs30 is valuable for crossbreeding and hybrid seed production. We then developed a new multi-control sterility system using ZmMs30 and its mutant line, and demonstrated it is feasible for generating desirable GMS lines and valuable for hybrid maize seed production. Taken together, our study sheds new light on the mechanisms of anther and pollen development, and provides a valuable male-sterility system for hybrid breeding maize.

Male sterile 305 Mutation Leads the Misregulation of Anther Cuticle Formation by Disrupting Lipid Metabolism in Maize

“…For the two ALDH genes of GRMZM2G090245 and GRMZM2G118800 in the lipid metabolism pathway, the former was found to be down regulated in ms305 anther during all three development stages (Table S2), while the latter was one of the top three hub genes in the PPI network (GRMZM2G118800, Figure 4B); and, previous studies found that ALDH activity was required for male fertility in plants [44,45]. We also found six GDSL lipases from the 42 DEGs in the lipid metabolism pathway, coincidentally, MS30 was reported to encode a GDSL lipase [15]. Taken together, these ALDH, GDSL lipases, and CYP450 superfamily genes would be involved in regulating lipid metabolism pathways as well as the cuticle metabolism in maize.…”

“…There are many types of abortion in maize GMS mutants, such as anther wall layer defects [15,16], abnormal meiosis of pollen mother cells [10], abnormal anther dehiscence [37], and abnormal callose degradation [38]. In the present study, the development of four somatic layers (epidermis, chamber wall, middle layer, and tapetum) of ms305 were delayed, and microspore abnormally degraded.…”

“…We hypothesize that delayed PCD of the inner four anther layers in ms305, including tapetum cells, leads to the degradation of pollen grains, and this should be responsible for its complete male sterility. Lipids play an important role in regulating plant anther development, a large number of studies have reported the role of fatty acids and their derivatives in regulating anther fertility [15,29,42]. For example, anther cuticle, including cutin and wax, can protect plant anthers from hydration [26].…”

“…In maize, MS45, MS26, MS30, MS33, IPE1, and APV1 are reported to participate in the aliphatic metabolic pathways, which are required for anther cuticle development [19,26,29,39,43]. The abortion characteristics of MS30, MS33, IPE1, and APV1 in maize were described, such as the swollen microspore and the decreased vacuole of APV1 at the vacuolated stage [19], severe degradation of the tapetum in IPE1 [20] and an obvious abortion of MS30 first appeared after the vacuolated stage [15], these were, however, different from ms305. In our study, ms305 also seriously affected the synthesis of anther cuticle and its monomers, as well as the content of soluble fatty acids in anthers.…”

“…However, only a handful of these genes have been cytologically characterized, and even fewer male sterile genes have been isolated. Moreover, over 50 GMS mutants in maize have been identified and characterized with the majority being recessive, such as ZmMs7 [9], Ms8 [10], Ms9 [11], Ms22/Msca1 [12], Ms23 [13], Ms26 [14], Ms30 [15], Ms32 [16], ZmMs33 [17], Ms45 [18], APV1 [19], IPE1 [20], MAC1 [21], and OCL4 [22]. The cloning and functional characterization of some male sterile genes have significantly contributed to our understanding of the molecular mechanisms of anther and pollen development in maize, which might provide useful genetic resources for hybrid maize seed production.…”