Developmental analysis of the early steps in strigolactone‐mediated axillary bud dormancy in rice

Abstract

SummaryBy contrast with rapid progress in understanding the mechanisms of biosynthesis and signaling of strigolactone (SL), mechanisms by which SL inhibits axillary bud outgrowth are less well understood. We established a rice (Oryza sativa L.) hydroponic culture system to observe axillary buds at the critical point when the buds enter the dormant state. In situ hybridization analysis indicated that cell division stops in the leaf primordia of the buds entering dormancy. We compared transcriptomes in the axillary buds isolated by laser capture microdissection before and after entering the dormant state and identified genes that are specifically upregulated or downregulated in dormant buds respectively, in SL‐mediated axillary bud dormancy. Typically, cell cycle genes and ribosomal genes are included among the active genes while abscisic acid (ABA)‐inducible genes are among the dormant genes. Application of ABA to the hydroponic culture suppressed the growth of axillary buds of SL mutants to the same level as wild‐type (WT) buds. Tiller number was decreased in the transgenic lines overexpressing OsNCED1, the gene that encodes ABA biosynthesis enzyme. These results indicated that the main site of SL function is the leaf primordia in the axillary bud and that ABA is involved in SL‐mediated axillary bud dormancy.

Comparing and Contrasting the Multiple Roles of Butenolide Plant Growth Regulators: Strigolactones and Karrikins in Plant Development and Adaptation to Abiotic Stresses

“…For instance, both SL and GA can affect internode elongation by stimulating cell division, but SL works independently of the GA signal in this process [177]. In addition, the roles of SL and GA in branch regulation are independent in pea [178]. GA 3 could significantly increase seed germination of kai2 and max2 mutants, indicating that KAI2 and MAX2 may not be involved in the stimulation of GA on seed germination [63].…”

Transcriptomic and physiological analyses of rice seedlings under different nitrogen supplies provide insight into the regulation involved in axillary bud outgrowth

“…In addition, genes involved in ABA biosynthesis and signalling were highly expressed in the axillary buds under HN, especially 5.0 mM N. A previous study revealed that the signalling regulators of ABA play roles in the response to ammonium toxicity [68], indicating that ABA should be involved in the axillary bud growth of plants under different N concentrations. Luo et al (2019) recently proposed that ABA suppresses the axillary bud growth of SL mutants and regulates SL-mediated axillary bud dormancy [69], suggesting that ABA may be involved in axillary bud dormancy to inhibit the bud outgrowth of plants under LN conditions. Genes related to the biosynthesis and degradation of GA were expressed at high and low levels, respectively, in the axillary buds under LN conditions.…”

Resolving the role of strigolactone in the early steps of rice axillary bud dormancy

“…Beyond this specific question the work presented by Luo et al . (), provides a highly important example of how hormone function contributes to the control of normal growth. Such insight is lacking not just for strigolactones but also for most other phytohormones.…”

“…Furthermore, evaluation of the transcriptomic data revealed that several ABA responsive genes as well as genes associated to ABA biosynthesis were induced on the transition to dormancy. Given this observation Luo et al (2019) next tested whether ABA suppresses bud outgrowth in rice by adding low concentrations of ABA which do not invoke major changes in plant growth. Intriguingly, while this addition of ABA did not affect tiller bud growth in wild-type plants it suppressed the growth of tiller buds in the strigolactone-deficient d10-1 mutant via an effect on cell division as well as their growth in the strigolactone signaling mutant d14-1.…”

“…However, the lack of congruence in the ABA levels of the strigolactone biosynthesis and signaling mutants, as well as how ABA and indeed strigolactone-mediated effects interact with the signals influencing axillary branching recently reported to emanate from the signal metabolite trehalose 6-phosphate (Fichtner et al, 2017), remains to be investigated. Beyond this specific question the work presented by Luo et al (2019), provides a highly important example of how hormone function contributes to the control of normal growth. Such insight is lacking not just for strigolactones but also for most other phytohormones.…”