Os03g0818800

The rice gene Os03g0818800 was reported as OsIDS1 in 2012.

Annotated Information

Function

• SNB and Oryza sativa INDETERMINATE SPIKELET 1 (OsIDS1) together play important roles in inflorescence architecture and the establishment of floral meristems.

Mutation

• Spikelets of osids1 were occasionally abnormal as compared with wild-type (WT) spikelets that consisted of one floret subtending two pairs of glumes – rudimentary glume and empty glume (Figure 1a; Arber, 1934). A normal floret comprises the flower proper (one pistil, six stamens, and two lodicules) plus a pair of bract-like organs (palea and lemma) (Figure 1e; Bommert et al., 2005). In the researchers' osids1 spikelets, one of the empty glumes was occasionally replaced by a rudimentary glume (Figure 1b), and 3.2% of those lodicules were elongated (Figure 1f, Table 1). An extra lodicule also was often found in mutant spikelets (Figure 1f, Table 1).

• To examine the functioning of OsIDS1 further, the researchers generated double mutants between osids1 and snb. Those had more bracts, including rudimentary glumes, lemma, and palea, than did single mutants (Figure 1b–d, Table 1). For example, osids1 and snb plants averaged 4.00 and 4.07 glumes, respectively, versus 4.67 in snb osids1. The number of lemma/palea was also increased, to 3.29 in the double mutant from 2.02 and 2.10 in the single mutants. The double mutants rarely developed empty glumes, but elongated bracts were occasionally found in the boundary between a rudimentary glume and lemma. However, their epidermis was similar to that of the lemma/palea (Figures 1d and S2b). Furthermore, ectopic structures were formed between their layers of lemma and palea, sometimes in a reiterated pattern (Figure 1i,j). Scanning electron microscopy (SEM) analyses revealed that these structures contained multiple rudimentary glumes, lemma/palea organs, and rachis (Figure S2c,d), suggesting that they were underdeveloped spikelets. These observations suggested that OsIDS1 functions together with SNB in spikelet development.

• The snb osids1 mutants also exhibited abnormal floral organs. Their most conspicuous feature was a change in the size and shape of the lodicules, with approximately 50% being elongated (Figure 1h, Table 1). Moreover, the surface of those elongated lodicules was transformed into those of the lemma and palea (Figure S2c,d). Ectopic lodicules were additionally formed at the side of the palea (Figure 1h), creating a concentric whorl with the original lodicules on the lemma side. These double mutants also had fewer stamens than the WT (Figure 1f–h, Table 1).

Figure 1. Spikelet phenotypes of snb, osids1, and snb osids1. (a) Wild-type (WT) spikelet. EG, empty glume; L, lemma; P, palea; RG, rudimentary glume. (b) osids1 spikelet. (c) snb spikelet. Arrows represent bract-like structure. L/P, lemma/palea-like structure. (d) snb osids1 spikelet. Red arrowhead indicates intermediate structure between lemma and glume. (e–h) Upper side of lemma and palea was removed to observe inner floral organs: (e) wild-type spikelet with two lodicules (Lo), six stamens (St), and one carpel (Ca); (f) osids1 spikelet with three elongated lodicules (Elo); (g) snb spikelet with two elongated lodicules, two normal lodicules, four stamens (St), and one carpel (Ca); (h) snb osids1 spikelet with four elongated lodicules. (i–k) Spikelets of snb osids1 double mutants showing ectopic spikelets (arrowheads). Ectopic spikelets were formed between layers of lemma/palea (i, j). Underdeveloped spikelets were formed reiteratively on flank of rachilla. Ectopic spikelet was formed on flank of carpel (k). .

Table 1 Phenotypic characterizations from different combinations of snb and osids1 alleles .

Expression

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Evolution

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Labs working on this gene

• Department of Plant Molecular Systems Biotechnology, Crop Biotech Institute, Kyung Hee University, Yongin 446-701, Korea