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LOOSE PLANT ARCHITECTURE 1 (LPA1) transcriptional repressor that promotes shoot erectness and reduces the tiller and leaf angle, resulting in a more compact plant. Thus, it is a positive regulator of shoot gravitropism that operates in the opposite direction of gravity. LPA1 is only involved in shoot gravitropism in rice, not root gravitropism. LPA1 is highly expressed in the lamina joint and internodes, especially in young tissues, and also expressed in older tiller base, coleoptile, root, seedling, and panicle but not much in the leaf blade and leaf sheath. The higher expression levels of LPA1 in the lamina joint and tiller node (Wu et al., 2013). LPA1 shows low expression in all three root zones of 4-day-old seedlings of O. sativa Nipponbare (Huang and Schiefelbein, 2015). However, the lpa1 mutant does not show any defects in root gravitropism. LPA1 regulates the tiller and leaf angles by controlling the adaxial growth of the tiller node and lamina joint. It determines lamina joint bending by suppressing auxin signaling (Dong et al., 2016), but it does not affect auxin asymmetry; thus, it does not overlap with LAZY1. Both LPA 1 and LAZY1 reduce the tiller angle. LAP1 is the functional ortholog of the AtIDD15/SHOOT GRAVITROPISM5 (SGR5) gene in Arabidopsis (Wu et al., 2013).
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