Genome-wide identification of the SnRK gene family in willow and expression analysis under abiotic stress

Drought and nitrogen (N) deposition significantly impact plant growth in northern regions. The balance between carbon (C) and N metabolism is crucial for plant adaptation to global environmental change. Salix gordejevii is widely distributed across the northern temperate zone and is characterized by rapid growth and high adaptability. However, the molecular mechanisms underlying its adaptation to drought and N deposition remain largely unclear. Sucrose non-fermenting 1-related protein kinases (SnRKs) represent a class of serine/threonine protein kinases that are extensively involved in plant C and N metabolism, as well as in responses to abiotic stress. We hypothesised that the SnRK gene family was essential for willow adaptation to drought and N deposition, with its evolutionary and structural features being closely linked to its stress-responsive expression patterns.

A total of 43 SpSnRK genes were identified and classified into three subfamilies: SpSnRK1 (2 members), SpSnRK2 (11 members), and SpSnRK3 (30 members). These genes exhibited an uneven distribution across the genome. Among them, 37 genes contained both coding and non-coding regions, while 6 consisted solely of coding regions. Most SpSnRK proteins were predicted to localize in the cytoplasm. The promoters of SpSnRK genes were found to be enriched with numerous stress- and hormone-responsive cis-acting elements. Furthermore, the SnRK genes expression profiles in leaves and roots were analyzed under four treatments (control, drought, N deposition, and a combination of drought and N deposition). The expression profile analysis revealed that, under drought stress or N deposition, a greater number of responsive SgSnRK genes were detected in the roots. However, under the combined conditions of drought and N deposition, the number of responsive SgSnRK genes increased significantly in the leaves.

The SnRK gene family in willow consisted of three subfamilies that exhibit structural differences and were unevenly distributed across the chromosomes. These genes played critical roles in multiple stress signaling pathways. Furthermore, their expression in response to drought and N deposition showed tissue specificity and varies according to the mode of stress combination.These findings provide a basis for further exploration of the molecular mechanisms underlying SnRK-associated abiotic stress responses.