Two AP2 family genes,SUPERNUMERARY BRACT(SNB) andOsINDETERMINATE SPIKELET 1(OsIDS1), synergistically control inflorescence architecture and floral meristem establishment in rice

Abstract

SUMMARYMeristem identity is crucial in determining the inflorescence architecture of grass species. We previously reported that SUPERNUMERARY BRACT (SNB) regulates the transition of spikelet meristems into floral meristems in rice (Oryza sativa). Here we demonstrated that SNB and Oryza sativa INDETERMINATE SPIKELET 1 (OsIDS1) together play important roles in inflorescence architecture and the establishment of floral meristems. In snb osids1 double mutants, the numbers of branches and spikelets within a panicle are significantly decreased, and the transition to a floral meristem is further delayed compared with the snb single mutant. Expression analyses showed that SNB and OsIDS1 are required for spatio-temporal expression of B-and E-function floral organ identity genes in the lodicules. In addition, the AP2 family genes are important for determining the degree of ramification in branch meristems, regulating the spatio-temporal expression of spikelet meristem genes, such as FRIZZY PANICLE (FZP). Furthermore, overexpression of microRNA172 (miR172) causes reductions in SNB and OsIDS1 transcript levels, and phenotypes of the transgenic plants are more severe than for snb osids1. This indicates that additional gene(s) participate in the development of branch and floral meristems. Preferential expression of mature miR172s in the area around the spikelet meristems implies that depletion of the AP2 family genes in those meristems via miR172 is an important step in controlling inflorescence branching and the formation of floral organs.

Short tandem target mimic rice lines uncover functions of miRNAs in regulating important agronomic traits

“…2H), and no abnormalities were observed in STTM172 flowers (SI Appendix, Fig. S5 A and B), in contrast to previous observations that overexpression of miR172 affected these features (31,32). STTM172 plants produced normal fertile pollen (SI Appendix, Fig.…”

“…miR172 has been the focus of multiple studies using different approaches, such as overexpression, expression of resistant target genes, or mutations in individual loci encoding the miRNA (26)(27)(28)(29)(30)(31)(32)(33)(34)(35). These previous studies suggested that miR172 mainly controls flowering time and floral organ identity.…”

“…For instance, loss of function of one locus, miR172a, and overexpression of miR172 targets resulted in slow vegetative development and late flowering in Arabidopsis (30), whereas overexpression of miR172 caused an early flowering phenotype and defective floral organ identity (9,26,30). Overexpression of miR172 in rice caused loss of spikelet determinacy and multiple abnormalities in floral organs, including an increased number of bract-like structures and multiple layers of lemma and palea, ultimately resulting in decreased fertility or even complete sterility (31,32).…”

Jasmonic acid regulates spikelet development in rice

“…Loss-of-function of OsMADS1 leads to reiterative formation of glumes or extra spikelet formation within spikelets, and defective organ identity 13,15 . In contrast to Arabidopsis, in which APETALA2 (AP2) genes play a role in specifying floral organ identity 9 , rice, maize and possibly other grasses use AP2/ERF-like genes to control spikelet meristem transition and deteminacy [16][17][18][19] . These findings suggest that grasses and dicots seem to use the same sets of genes in different aspects of meristem identity specification in reproduction.…”

Genome-Wide Targets Regulated by the OsMADS1 Transcription Factor Reveals Its DNA Recognition Properties

“…Moreover, Arabidopsis SEP3 also directly influences ANT expression in differentiating Arabidopsis floral organs (Pajoro et al, 2014b). Rice has five genes closely related to Arabidopsis AP2 (Tang et al, 2007), including SUPERNUMERARY BRACT and INDETERMINATE SPIKELET1, mutants of which indicate critical roles in rice FM specification and floret organ development (Lee and An, 2012). We find that the rice AP2-like factor gene Os04g55560 is directly and negatively regulated by OsMADS1.…”