Aliphatic alcohols naturally exist in many organisms as important cellular components; however, their roles in extracellular polymer biosynthesis are poorly defined. We report here the isolation and characterization of a rice (Oryza sativa) malesterile mutant, defective pollen wall (dpw), which displays defective anther development and degenerated pollen grains with an irregular exine. Chemical analysis revealed that dpw anthers had a dramatic reduction in cutin monomers and an altered composition of cuticular wax, as well as soluble fatty acids and alcohols. Using map-based cloning, we identified the DPW gene, which is expressed in both tapetal cells and microspores during anther development. Biochemical analysis of the recombinant DPW enzyme shows that it is a novel fatty acid reductase that produces 1-hexadecanol and exhibits >270-fold higher specificity for palmiltoyl-acyl carrier protein than for C16:0 CoA substrates. DPW was predominantly targeted to plastids mediated by its N-terminal transit peptide. Moreover, we demonstrate that the monocot DPW from rice complements the dicot Arabidopsis thaliana male sterile2 (ms2) mutant and is the probable ortholog of MS2. These data suggest that DPWs participate in a conserved step in primary fatty alcohol synthesis for anther cuticle and pollen sporopollenin biosynthesis in monocots and dicots.

To understand the molecular mechanism regulating meristem development in the monocot rice (Oryza sativa), we describe here the isolation and characterization of three floral organ number4 (fon4) alleles and the cloning of the FON4 gene. The fon4 mutants showed abnormal enlargement of the embryonic and vegetative shoot apical meristems (SAMs) and the inflorescence and floral meristems. Likely due to enlarged SAMs, fon4 mutants produced thick culms (stems) and increased numbers of both primary rachis branches and floral organs. We identified FON4 using a map-based cloning approach and found it encodes a small putatively secreted protein, which is the putative ortholog of the Arabidopsis (Arabidopsis thaliana) CLAVATA3 (CLV3) gene. FON4 transcripts mainly accumulated in the small group of cells at the apex of the SAMs, whereas the rice ortholog of CLV1 (FON1) is expressed throughout the SAMs, suggesting that the putative FON4 ligand might be sequestered as a possible mechanism for rice meristem regulation. Exogenous application of the peptides FON4p and CLV3p corresponding to the CLV3/ESR-related (CLE) motifs of FON4 and CLV3, respectively, resulted in termination of SAMs in rice, and treatment with CLV3p caused consumption of both rice and Arabidopsis root meristems, suggesting that the CLV pathway in limiting meristem size is conserved in both rice and Arabidopsis. However, exogenous FON4p did not have an obvious effect on limiting both rice and Arabidopsis root meristems, suggesting that the CLE motifs of Arabidopsis CLV3 and FON4 are potentially functionally divergent.

Multicellular organisms contain a large number of formins; however, their physiological roles in plants remain poorly understood. Here, we reveal that formin homology 5 (FH5), a type II formin mutated in rice morphology determinant (rmd), plays a crucial role in determining rice (Oryza sativa) morphology. FH5/RMD encodes a formin-like protein consisting of an N-terminal phosphatase tensin (PTEN)-like domain, an FH1 domain, and an FH2 domain. The rmd mutants display a bending growth pattern in seedlings, are stunted as adult plants, and have aberrant inflorescence (panicle) and seed shape. Cytological analysis showed that rmd mutants have severe cell elongation defects and abnormal microtubule and microfilament arrays. FH5/RMD is ubiquitously expressed in rice tissues, and its protein localization to the chloroplast surface is mediated by the PTEN domain. Biochemical assays demonstrated that recombinant FH5 protein can nucleate actin polymerization from monomeric G-actin or actin/profilin complexes, cap the barbed end of actin filaments, and bundle actin filaments in vitro. Moreover, FH5 can directly bind to and bundle microtubules through its FH2 domain in vitro. Our findings suggest that the rice formin protein FH5 plays a critical role in determining plant morphology by regulating actin dynamics and proper spatial organization of microtubules and microfilaments.

Rosmarinic acid (RA) and lithospermic acid B (LAB) are two typical phenolic acids with significant bioactivities that may contribute to the therapeutic effects of Salvia miltiorrhiza. Precise knowledge of the biosynthetic pathway leading to RA and LAB is a necessary prerequisite to optimize the production of important phenolic compounds in S. miltiorrhiza. In vivo isotopic labeling experiments using [ring-(13)C]-phenylalanine, combined with dynamic measurements of metabolite levels by UPLC/Q-TOF, were used to investigate the metabolic origin of phenolic acids in S. miltiorrhiza. These data indicate the in vivo phenolic biosynthetic pathway: two intermediates from the general phenylpropanoid pathway and the tyrosine-derived pathway, 4-coumaroyl-CoA and 3,4-dihydroxyphenyllactic acid (DHPL), are coupled by the ester-forming enzyme rosmarinic acid synthase (SmRAS) to form 4-coumaroyl-3',4'-dihydroxyphenyllactic acid (4C-DHPL). The 3-hydroxyl group is introduced late in the pathway by a cytochrome P450-dependent monooxygenase (SmCYP98A14) to form RA. Subsequently, RA is transformed to a phenoxyl radical by oxidation, and two phenoxyl radicals unite spontaneously to form LAB. The results indicate aspects of the complexity of phenolic acid biosynthesis in S. miltiorrhiza and expand an understanding of phenylpropanoid-derived metabolic pathways. The candidate genes for the key enzymes that were revealed provide a substantial foundation for follow-up research on improving the production of important phenolic acids through metabolic engineering in the future.

Trichomes, small protrusions on the surface of many plant species, can produce and store various secondary metabolic products. Artemisinin, the most famous and potent medicine for malaria, is synthesized, stored, and secreted by Artemisia annua trichomes. However, the molecular basis regulating the biosynthesis of artemisinin and the development of trichomes in A. annua remains poorly understood. Here, we report that an AP2 transcription factor, TRICHOME AND ARTEMISININ REGULATOR 1 (TAR1), plays crucial roles in regulating the development of trichomes and the biosynthesis of artemisinin in A. annua. TAR1, which encodes a protein specially located in the nucleus, is mainly expressed in young leaves, flower buds, and some trichomes. In TAR1-RNAi lines, the morphology of trichomes and the composition of cuticular wax were altered, and the artemisinin content was dramatically reduced, which could be significantly increased by TAR1 oeverexpression. Expression levels of several key genes that are involved in artemisinin biosynthesis were altered when TAR1 was silenced or overexpressed. By the electrophoretic mobility shift, yeast one-hybrid and transient transformation β-glucuronidase assays, we showed that ADS and CYP71AV1, two key genes in the biosynthesis pathway of artemisinin, are likely the direct targets of TAR1. Taken together, our results indicate that TAR1 is a key component of the molecular network regulating trichome development and artemisinin biosynthesis in A. annua.

Salvia miltiorrhiza Bunge, which contains tanshinones and phenolic acids as major classes of bioactive components, is one of the most widely used herbs in traditional Chinese medicine. Production of tanshinones and phenolic acids is enhanced by methyl jasmonate (MeJA). Transcription factor MYC2 is the switch of jasmontes signaling in plants. Here, we focused on two novel JA-inducible genes in S. miltiorrhiza, designated as SmMYC2a and SmMYC2b, which were localized in the nucleus. SmMYC2a and SmMYC2b were also discovered to interact with SmJAZ1 and SmJAZ2, implying that the two MYC2s might function as direct targets of JAZ proteins. Ectopic RNA interference (RNAi)-mediated knockdown experiments suggested that SmMYC2a/b affected multiple genes in tanshinone and phenolic acid biosynthetic pathway. Besides, the accumulation of tanshinones and phenolic acids was impaired by the loss of function in SmMYC2a/b. Meanwhile, SmMYC2a could bind with an E-box motif within SmHCT6 and SmCYP98A14 promoters, while SmMYC2b bound with an E-box motif within SmCYP98A14 promoter, through which the regulation of phenolic acid biosynthetic pathway might achieve. Together, these results suggest that SmMYC2a and SmMYC2b are JAZ-interacting transcription factors that positively regulate the biosynthesis of tanshinones and Sal B with similar but irreplaceable effects.

In flowering plants, formation of the haploid male gametophytes in anthers requires the interaction between reproductive cells and the neighboring somatic cells, yet the underlying mechanism remains poorly understood. Here, we reveal the crucial role of a fasciclin glycoprotein, MICROSPORE AND TAPETUM REGULATOR1 (MTR1), in controlling the development of sporophytic and reproductive cells in rice (Oryza sativa). MTR1 is specifically expressed in the male reproductive cells, yet its mutant exhibits defects in both tapetum and microspore development, causing complete male sterility. We also demonstrate that the fasciclin domains, N-glycolation, and N-terminal signal peptide-mediated plasma membrane localization of MTR1 are required for normal anther development and pollen fertility. Our findings show that rice male reproductive cells secrete the MTR1 protein to control the development of reproductive cells and their adjacent somatic cells, thus providing novel insights into the mechanism of plant male reproductive development.

Root angle has a major impact on acquisition of nutrients like phosphate that accumulate in topsoil and in many species; low phosphate induces shallower root growth as an adaptive response. Identifying genes and mechanisms controlling root angle is therefore of paramount importance to plant breeding. Here we show that the actin-binding protein Rice Morphology Determinant (RMD) controls root growth angle by linking actin filaments and gravity-sensing organelles termed statoliths. RMD is upregulated in response to low external phosphate and mutants lacking of RMD have steeper crown root growth angles that are unresponsive to phosphate levels. RMD protein localizes to the surface of statoliths, and rmd mutants exhibit faster gravitropic response owing to more rapid statoliths movement. We conclude that adaptive changes to root angle in response to external phosphate availability are RMD dependent, providing a potential target for breeders.