Rice CYP703A3, a cytochrome P450 hydroxylase, is essential for development of anther cuticle and pollen exine

Abstract

Anther cuticle and pollen exine act as protective envelopes for the male gametophyte or pollen grain, but the mechanism underlying the synthesis of these lipidic polymers remains unclear. Previously, a tapetum-expressed CYP703A3, a putative cytochrome P450 fatty acid hydroxylase, was shown to be essential for male fertility in rice (Oryza sativa L.). However, the biochemical and biological roles of CYP703A3 has not been characterized. Here, we observed that cyp703a3-2 caused by one base insertion in CYP703A3 displays defective pollen exine and anther epicuticular layer, which differs from Arabidopsis cyp703a2 in which only defective pollen exine occurs. Consistently, chemical composition assay showed that levels of cutin monomers and wax components were dramatically reduced in cyp703a3-2 anthers. Unlike the wide range of substrates of Arabidopsis CYP703A2, CYP703A3 functions as an in-chain hydroxylase only for a specific substrate, lauric acid, preferably generating 7-hydroxylated lauric acid. Moreover, chromatin immunoprecipitation and expression analyses revealed that the expression of CYP703A3 is directly regulated by Tapetum Degeneration Retardation, a known regulator of tapetum PCD and pollen exine formation. Collectively, our results suggest that CYP703A3 represents a conserved and diversified biochemical pathway for in-chain hydroxylation of lauric acid required for the development of male organ in higher plants.

Two ATP Binding Cassette G (ABCG) Transporters, OsABCG26 and OsABCG15, Collaboratively Regulate Rice Male Reproduction

“…Previous reports showed that plastids could not been found in anther epidermal cells (Mamun et al, 2005a(Mamun et al, , 2005b, which implies that lipid de novo synthesis cannot occur within anther epidermal cells. Therefore, it is not surprising that several tapetum-expressed lipid metabolism genes are involved in anther cuticle formation (Li et al, 2010;Shi et al, 2011;Yang et al, 2014). Here, we observed that OsABCG26 is localized to the plasma membrane of anther wall layers at stage 9 during anther development, and mutation of OsABCG26 leads to detective anther cuticle and pollen exine, suggesting that cuticular lipids are produced in the tapetum, from which they are exported or distributed by OsABCG26.…”

“…It is generally accepted that sporopollenin, the pollen exine constituent, is produced exclusively in tapetum, and many genes involved in lipid synthesis and exine formation were identified in tapetum (Li et al, 2010;Quilichini et al, 2010Quilichini et al, , 2014Ariizumi and Toriyama, 2011;Chen et al, 2011b;Shi et al, 2011;Zhu et al, 2013;Lou et al, 2014;Yang et al, 2014). However, there is no Figure 11.…”

“…Up to date, some tapetum-expressed proteins, such as cytochrome P450s (CYP450s; Li et al, 2010;Yang et al, 2014), fatty acyl carrier protein (ACP) reductase (Shi et al, 2011), ABCG transporters (Niu et al, 2013a;Qin et al, 2013;Zhu et al, 2013;Wu et al, 2014), LTPs , and basic helix-loophelix (bHLH) transcription factors (Li et al, 2006;Zhang et al, 2008;Niu et al, 2013b), have been identified to be involved in anther cuticle and pollen exine development in rice. CYP704B2 functions as a v-hydroxylase in producing v-hydroxylated fatty acids with 16 and 18 carbon chains as the common precursors of two biopolymers: sporopollenin and cutin (Li et al, 2010).…”

“…OsC6 (for locus [LOC]_Os11g37280) belongs to the small LTP protein family, and it is expressed in tapetal cells and involved in the mediation of lipidic distribution from the tapetal cytoplasm to the extracellular space among different anther cell wall layers and to the anther locules and anther cuticle . The bHLH transcription factor Tapetum Degeneration Retardation (TDR) and its ortholog in Arabidopsis (Arabidopsis thaliana) ABORTED MICROSPORES (AMS) both play a critical role in directly promoting the expression of genes associated with sporopollenin biosynthesis and the secretion of materials for pollen wall patterning (Zhang et al, 2008;Xu et al, 2010Xu et al, , 2014Yang et al, 2014;Zhang and Li, 2014). Mutation or knockdown of all of these genes caused male sterility and defective anther cuticle and pollen exine (Li et al, 2010;Shi et al, 2011;Niu et al, 2013aNiu et al, , 2013bQin et al, 2013;Zhu et al, 2013;Wu et al, 2014;Yang et al, 2014).…”

“…The tapetum, the innermost layer of the four anther cell wall layers, is considered the site of pollen sporopollenin and anther cuticle precursor synthesis, at least in the monocot model plant rice (Oryza sativa; Yang et al, 2014). Up to date, some tapetum-expressed proteins, such as cytochrome P450s (CYP450s; Li et al, 2010;Yang et al, 2014), fatty acyl carrier protein (ACP) reductase (Shi et al, 2011), ABCG transporters (Niu et al, 2013a;Qin et al, 2013;Zhu et al, 2013;Wu et al, 2014), LTPs , and basic helix-loophelix (bHLH) transcription factors (Li et al, 2006;Zhang et al, 2008;Niu et al, 2013b), have been identified to be involved in anther cuticle and pollen exine development in rice.…”