The Altered Responses of a New Mutant long life span 1 to Cytokinin in Arabidopsis thaliana

Cytokinins are a class of essential plant hormones regulating plant growth and development. Although the two-component phosphorelay pathway of cytokinin has been well characterized, the intact cytokinin responses regulation picture still needs to be fully depicted. Here we report a new mutant, long life span 1 (lls1), which displays dwarf stature, curled leaves, numerous axillary branches and nearly 5-month life span. Exogenous cytokinin could not recover the phenotypes of the mutant. Moreover, mutation in lls1 suppressed the cytokinin-responsive phenotypes, including root and hypocotyl growth inhibition, anthocyanin accumulation, metaxylem promotion in primary root development. The induction of cytokinin-responsive genes, ARR5, AHP5, and CKX3, was also suppressed in lls1. According to quantitative RT-PCR (qRT-PCR) and microarray results, the basal expression of positive factors AHP5, ARR1, and ARR10 were down-regulated, while the negative factors ARR4 and ARR5 were up-regulated. Our results suggested that LLS1 gene might be involved in the regulation of cytokinin signaling. It was mapped to chromosome 4 where no other cytokinin relevant gene has been reported.