Tillering and small grain 1 dominates the tryptophan aminotransferase family required for local auxin biosynthesis in rice

Abstract

Auxin is a crucial phytohormone, controlling multiple aspects of plant growth and responses to the changing environment. However, the role of local auxin biosynthesis in specific developmental programs remains unknown in crops. This study characterized the rice tillering and small grain 1 (tsg1) mutant, which has more tillers but a smaller panicle and grain size resulting from a reduction in endogenous auxin. TSG1 encodes a tryptophan aminotransferase that is allelic to the FISH BONE (FIB) gene. The tsg1 mutant showed hypersensitivity to indole-3-acetic acid and the competitive inhibitor of aminotransferase, L-kynurenine. TSG1 knockout resulted in an increased tiller number but reduction in grain number and size, and decrease in height. Meanwhile, deletion of the TSG1 homologs OsTAR1, OsTARL1, and OsTARL2 caused no obvious changes, although the phenotype of the TSG1/OsTAR1 double mutant was intensified and infertile, suggesting gene redundancy in the rice tryptophan aminotransferase family. Interestingly, TSG1 and OsTAR1, but not OsTARL1 and OsTARL2, displayed marked aminotransferase activity. Meanwhile, subcellular localization was identified as the endoplasmic reticulum, while phylogenetic analysis revealed functional divergence of TSG1 and OsTAR1 from OsTARL1 and OsTARL2. These findings suggest that TSG1 dominates the tryptophan aminotransferase family, playing a prominent role in local auxin biosynthesis in rice.

UDP-glucosyltransferase regulates grain size and abiotic stress tolerance associated with metabolic flux redirection in rice

“…Enhanced expression of Big Grain 1 (BG1), which is a positive regulator of auxin response and transport results in extra-large grains 48 . Moreover, plants with mutation in TILLERING AND SMALL GRAIN 1 (TSG1), which controls local auxin biosynthesis and affect auxin signaling and transport, exhibit small grains as a result of disruption of localized cell proliferation and cell expansion 36 . Consistent with these previous studies linking auxin to grain size, we found that GSA1 regulates grain size by finely modulating cell proliferation and cell expansion during different stages of spikelet development (Fig.…”

“…2i). Interestingly, the expression level of TSG1, which controls grain size by regulating local auxin biosynthesis 36 , was significantly decreased in NIL-GSA1 CG14 ; the expression levels of the TSG1 homologs OsTAR1, OsTARL1, and OsTARL2 were also decreased ( Fig. 2i).…”

“…Plant growth and development are largely influenced by auxin, and a recent study revealed that the disruption of local auxin biosynthesis in rice affects auxin signaling and transport, as well as localized cell proliferation and cell expansion, resulting in smaller grains 36 . Given that GSA1 is responsible for cell proliferation and cell expansion and regulates spikelet development, we asked whether local auxin biosynthesis, signaling and transport are disrupted in NIL-GSA CG14 .…”

Expression of TaTAR2.3-1B, TaYUC9-1 and TaYUC10 correlates with auxin and starch content of developing wheat grains

“…The promotive effect of TAR and IAA for grain fill in wheat is supported by the positive effect on grain yield of TaTAR2.1-3A overexpression (Shao et al 2017). In addition, a mutant of the orthologous gene, tsg1, has a negative effect on grain size in rice (Guo et al 2019).…”

“…For example, the shrunken grain phenotype of defective endosperm and defective kernel mutants of maize, de18 and dek18 appears to result from low levels of IAA in the developing grains caused by mutations affecting ZmYUC1 expression (Bernardi et al 2012;Bernardi et al 2016). In rice, a mutation in the IAA biosynthesis gene OsTAR2/FIB is associated with the tillering and small grain 1 (tsg1) phenotype (Guo et al 2019). Finally, in wheat, Shao et al (2017) showed that overexpression of TaTAR2.1-3A…”